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  <title>P0323R6: std::expected</title>
<style data-fill-with="stylesheet">/******************************************************************************
 *                   Style sheet for the W3C specifications                   *
 *
 * Special classes handled by this style sheet include:
 *
 * Indices
 *   - .toc for the Table of Contents (<ol class="toc">)
 *     + <span class="secno"> for the section numbers
 *   - #toc for the Table of Contents (<nav id="toc">)
 *   - ul.index for Indices (<a href="#ref">term</a><span>, in §N.M</span>)
 *   - table.index for Index Tables (e.g. for properties or elements)
 *
 * Structural Markup
 *   - table.data for general data tables
 *     -> use 'scope' attribute, <colgroup>, <thead>, and <tbody> for best results !
 *     -> use <table class='complex data'> for extra-complex tables
 *     -> use <td class='long'> for paragraph-length cell content
 *     -> use <td class='pre'> when manual line breaks/indentation would help readability
 *   - dl.switch for switch statements
 *   - ol.algorithm for algorithms (helps to visualize nesting)
 *   - .figure and .caption (HTML4) and figure and figcaption (HTML5)
 *     -> .sidefigure for right-floated figures
 *   - ins/del
 *
 * Code
 *   - pre and code
 *
 * Special Sections
 *   - .note       for informative notes             (div, p, span, aside, details)
 *   - .example    for informative examples          (div, p, pre, span)
 *   - .issue      for issues                        (div, p, span)
 *   - .assertion  for assertions                    (div, p, span)
 *   - .advisement for loud normative statements     (div, p, strong)
 *   - .annoying-warning for spec obsoletion notices (div, aside, details)
 *
 * Definition Boxes
 *   - pre.def   for WebIDL definitions
 *   - table.def for tables that define other entities (e.g. CSS properties)
 *   - dl.def    for definition lists that define other entitles (e.g. HTML elements)
 *
 * Numbering
 *   - .secno for section numbers in .toc and headings (<span class='secno'>3.2</span>)
 *   - .marker for source-inserted example/figure/issue numbers (<span class='marker'>Issue 4</span>)
 *   - ::before styled for CSS-generated issue/example/figure numbers:
 *     -> Documents wishing to use this only need to add
 *        figcaption::before,
 *        .caption::before { content: "Figure "  counter(figure) " ";  }
 *        .example::before { content: "Example " counter(example) " "; }
 *        .issue::before   { content: "Issue "   counter(issue) " ";   }
 *
 * Header Stuff (ignore, just don't conflict with these classes)
 *   - .head for the header
 *   - .copyright for the copyright
 *
 * Miscellaneous
 *   - .overlarge for things that should be as wide as possible, even if
 *     that overflows the body text area. This can be used on an item or
 *     on its container, depending on the effect desired.
 *     Note that this styling basically doesn't help at all when printing,
 *     since A4 paper isn't much wider than the max-width here.
 *     It's better to design things to fit into a narrower measure if possible.
 *   - js-added ToC jump links (see fixup.js)
 *
 ******************************************************************************/

/******************************************************************************/
/*                                   Body                                     */
/******************************************************************************/

	body {
		counter-reset: example figure issue;

		/* Layout */
		max-width: 50em;               /* limit line length to 50em for readability   */
		margin: 0 auto;                /* center text within page                     */
		padding: 1.6em 1.5em 2em 50px; /* assume 16px font size for downlevel clients */
		padding: 1.6em 1.5em 2em calc(26px + 1.5em); /* leave space for status flag     */

		/* Typography */
		line-height: 1.5;
		font-family: sans-serif;
		widows: 2;
		orphans: 2;
		word-wrap: break-word;
		overflow-wrap: break-word;
		hyphens: auto;

		/* Colors */
		color: black;
		background: white top left fixed no-repeat;
		background-size: 25px auto;
	}


/******************************************************************************/
/*                         Front Matter & Navigation                          */
/******************************************************************************/

/** Header ********************************************************************/

	div.head { margin-bottom: 1em }
	div.head hr { border-style: solid; }

	div.head h1 {
		font-weight: bold;
		margin: 0 0 .1em;
		font-size: 220%;
	}

	div.head h2 { margin-bottom: 1.5em;}

/** W3C Logo ******************************************************************/

	.head .logo {
		float: right;
		margin: 0.4rem 0 0.2rem .4rem;
	}

	.head img[src*="logos/W3C"] {
		display: block;
		border: solid #1a5e9a;
		border-width: .65rem .7rem .6rem;
		border-radius: .4rem;
		background: #1a5e9a;
		color: white;
		font-weight: bold;
	}

	.head a:hover > img[src*="logos/W3C"],
	.head a:focus > img[src*="logos/W3C"] {
		opacity: .8;
	}

	.head a:active > img[src*="logos/W3C"] {
		background: #c00;
		border-color: #c00;
	}

	/* see also additional rules in Link Styling section */

/** Copyright *****************************************************************/

	p.copyright,
	p.copyright small { font-size: small }

/** Back to Top / ToC Toggle **************************************************/

	@media print {
		#toc-nav {
			display: none;
		}
	}
	@media not print {
		#toc-nav {
			position: fixed;
			z-index: 2;
			bottom: 0; left: 0;
			margin: 0;
			min-width: 1.33em;
			border-top-right-radius: 2rem;
			box-shadow: 0 0 2px;
			font-size: 1.5em;
			color: black;
		}
		#toc-nav > a {
			display: block;
			white-space: nowrap;

			height: 1.33em;
			padding: .1em 0.3em;
			margin: 0;

			background: white;
			box-shadow: 0 0 2px;
			border: none;
			border-top-right-radius: 1.33em;
			background: white;
		}
		#toc-nav > #toc-jump {
			padding-bottom: 2em;
			margin-bottom: -1.9em;
		}

		#toc-nav > a:hover,
		#toc-nav > a:focus {
			background: #f8f8f8;
		}
		#toc-nav > a:not(:hover):not(:focus) {
			color: #707070;
		}

		/* statusbar gets in the way on keyboard focus; remove once browsers fix */
		#toc-nav > a[href="#toc"]:not(:hover):focus:last-child {
			padding-bottom: 1.5rem;
		}

		#toc-nav:not(:hover) > a:not(:focus) > span + span {
			/* Ideally this uses :focus-within on #toc-nav */
			display: none;
		}
		#toc-nav > a > span + span {
			padding-right: 0.2em;
		}

		#toc-toggle-inline {
			vertical-align: 0.05em;
			font-size: 80%;
			color: gray;
			color: hsla(203,20%,40%,.7);
			border-style: none;
			background: transparent;
			position: relative;
		}
		#toc-toggle-inline:hover:not(:active),
		#toc-toggle-inline:focus:not(:active) {
			text-shadow: 1px 1px silver;
			top: -1px;
			left: -1px;
		}

		#toc-nav :active {
			color: #C00;
		}
	}

/** ToC Sidebar ***************************************************************/

	/* Floating sidebar */
	@media screen {
		body.toc-sidebar #toc {
			position: fixed;
			top: 0; bottom: 0;
			left: 0;
			width: 23.5em;
			max-width: 80%;
			max-width: calc(100% - 2em - 26px);
			overflow: auto;
			padding: 0 1em;
			padding-left: 42px;
			padding-left: calc(1em + 26px);
			background: inherit;
			background-color: #f7f8f9;
			z-index: 1;
			box-shadow: -.1em 0 .25em rgba(0,0,0,.1) inset;
		}
		body.toc-sidebar #toc h2 {
			margin-top: .8rem;
			font-variant: small-caps;
			font-variant: all-small-caps;
			text-transform: lowercase;
			font-weight: bold;
			color: gray;
			color: hsla(203,20%,40%,.7);
		}
		body.toc-sidebar #toc-jump:not(:focus) {
			width: 0;
			height: 0;
			padding: 0;
			position: absolute;
			overflow: hidden;
		}
	}
	/* Hide main scroller when only the ToC is visible anyway */
	@media screen and (max-width: 28em) {
		body.toc-sidebar {
			overflow: hidden;
		}
	}

	/* Sidebar with its own space */
	@media screen and (min-width: 78em) {
		body:not(.toc-inline) #toc {
			position: fixed;
			top: 0; bottom: 0;
			left: 0;
			width: 23.5em;
			overflow: auto;
			padding: 0 1em;
			padding-left: 42px;
			padding-left: calc(1em + 26px);
			background: inherit;
			background-color: #f7f8f9;
			z-index: 1;
			box-shadow: -.1em 0 .25em rgba(0,0,0,.1) inset;
		}
		body:not(.toc-inline) #toc h2 {
			margin-top: .8rem;
			font-variant: small-caps;
			font-variant: all-small-caps;
			text-transform: lowercase;
			font-weight: bold;
			color: gray;
			color: hsla(203,20%,40%,.7);
		}

		body:not(.toc-inline) {
			padding-left: 29em;
		}
		/* See also Overflow section at the bottom */

		body:not(.toc-inline) #toc-jump:not(:focus) {
			width: 0;
			height: 0;
			padding: 0;
			position: absolute;
			overflow: hidden;
		}
	}
	@media screen and (min-width: 90em) {
		body:not(.toc-inline) {
			margin: 0 4em;
		}
	}

/******************************************************************************/
/*                                Sectioning                                  */
/******************************************************************************/

/** Headings ******************************************************************/

	h1, h2, h3, h4, h5, h6, dt {
		page-break-after: avoid;
		page-break-inside: avoid;
		font: 100% sans-serif;   /* Reset all font styling to clear out UA styles */
		font-family: inherit;    /* Inherit the font family. */
		line-height: 1.2;        /* Keep wrapped headings compact */
		hyphens: manual;         /* Hyphenated headings look weird */
	}

	h2, h3, h4, h5, h6 {
		margin-top: 3rem;
	}

	h1, h2, h3 {
		color: #005A9C;
		background: transparent;
	}

	h1 { font-size: 170%; }
	h2 { font-size: 140%; }
	h3 { font-size: 120%; }
	h4 { font-weight: bold; }
	h5 { font-style: italic; }
	h6 { font-variant: small-caps; }
	dt { font-weight: bold; }

/** Subheadings ***************************************************************/

	h1 + h2,
	#subtitle {
		/* #subtitle is a subtitle in an H2 under the H1 */
		margin-top: 0;
	}
	h2 + h3,
	h3 + h4,
	h4 + h5,
	h5 + h6 {
		margin-top: 1.2em; /* = 1 x line-height */
	}

/** Section divider ***********************************************************/

	:not(.head) > hr {
		font-size: 1.5em;
		text-align: center;
		margin: 1em auto;
		height: auto;
		border: transparent solid 0;
		background: transparent;
	}
	:not(.head) > hr::before {
		content: "\2727\2003\2003\2727\2003\2003\2727";
	}

/******************************************************************************/
/*                            Paragraphs and Lists                            */
/******************************************************************************/

	p {
		margin: 1em 0;
	}

	dd > p:first-child,
	li > p:first-child {
		margin-top: 0;
	}

	ul, ol {
		margin-left: 0;
		padding-left: 2em;
	}

	li {
		margin: 0.25em 0 0.5em;
		padding: 0;
	}

	dl dd {
		margin: 0 0 .5em 2em;
	}

	.head dd + dd { /* compact for header */
		margin-top: -.5em;
	}

	/* Style for algorithms */
	ol.algorithm ol:not(.algorithm),
	.algorithm > ol ol:not(.algorithm) {
	 border-left: 0.5em solid #DEF;
	}

	/* Put nice boxes around each algorithm. */
	[data-algorithm]:not(.heading) {
	  padding: .5em;
	  border: thin solid #ddd; border-radius: .5em;
	  margin: .5em calc(-0.5em - 1px);
	}
	[data-algorithm]:not(.heading) > :first-child {
	  margin-top: 0;
	}
	[data-algorithm]:not(.heading) > :last-child {
	  margin-bottom: 0;
	}

	/* Style for switch/case <dl>s */
	dl.switch > dd > ol.only,
	dl.switch > dd > .only > ol {
	 margin-left: 0;
	}
	dl.switch > dd > ol.algorithm,
	dl.switch > dd > .algorithm > ol {
	 margin-left: -2em;
	}
	dl.switch {
	 padding-left: 2em;
	}
	dl.switch > dt {
	 text-indent: -1.5em;
	 margin-top: 1em;
	}
	dl.switch > dt + dt {
	 margin-top: 0;
	}
	dl.switch > dt::before {
	 content: '\21AA';
	 padding: 0 0.5em 0 0;
	 display: inline-block;
	 width: 1em;
	 text-align: right;
	 line-height: 0.5em;
	}

/** Terminology Markup ********************************************************/


/******************************************************************************/
/*                                 Inline Markup                              */
/******************************************************************************/

/** Terminology Markup ********************************************************/
	dfn   { /* Defining instance */
		font-weight: bolder;
	}
	a > i { /* Instance of term */
		font-style: normal;
	}
	dt dfn code, code.idl {
		font-size: medium;
	}
	dfn var {
		font-style: normal;
	}

/** Change Marking ************************************************************/

	del { color: red;  text-decoration: line-through; }
	ins { color: #080; text-decoration: underline;    }

/** Miscellaneous improvements to inline formatting ***************************/

	sup {
		vertical-align: super;
		font-size: 80%
	}

/******************************************************************************/
/*                                    Code                                    */
/******************************************************************************/

/** General monospace/pre rules ***********************************************/

	pre, code, samp {
		font-family: Menlo, Consolas, "DejaVu Sans Mono", Monaco, monospace;
		font-size: .9em;
		page-break-inside: avoid;
		hyphens: none;
		text-transform: none;
	}
	pre code,
	code code {
		font-size: 100%;
	}

	pre {
		margin-top: 1em;
		margin-bottom: 1em;
		overflow: auto;
	}

/** Inline Code fragments *****************************************************/

  /* Do something nice. */

/******************************************************************************/
/*                                    Links                                   */
/******************************************************************************/

/** General Hyperlinks ********************************************************/

	/* We hyperlink a lot, so make it less intrusive */
	a[href] {
		color: #034575;
		text-decoration: none;
		border-bottom: 1px solid #707070;
		/* Need a bit of extending for it to look okay */
		padding: 0 1px 0;
		margin: 0 -1px 0;
	}
	a:visited {
		border-bottom-color: #BBB;
	}

	/* Use distinguishing colors when user is interacting with the link */
	a[href]:focus,
	a[href]:hover {
		background: #f8f8f8;
		background: rgba(75%, 75%, 75%, .25);
		border-bottom-width: 3px;
		margin-bottom: -2px;
	}
	a[href]:active {
		color: #C00;
		border-color: #C00;
	}

	/* Backout above styling for W3C logo */
	.head .logo,
	.head .logo a {
		border: none;
		text-decoration: none;
		background: transparent;
	}

/******************************************************************************/
/*                                    Images                                  */
/******************************************************************************/

	img {
		border-style: none;
	}

	/* For autogen numbers, add
	   .caption::before, figcaption::before { content: "Figure " counter(figure) ". "; }
	*/

	figure, .figure, .sidefigure {
		page-break-inside: avoid;
		text-align: center;
		margin: 2.5em 0;
	}
	.figure img,    .sidefigure img,    figure img,
	.figure object, .sidefigure object, figure object {
		max-width: 100%;
		margin: auto;
	}
	.figure pre, .sidefigure pre, figure pre {
		text-align: left;
		display: table;
		margin: 1em auto;
	}
	.figure table, figure table {
		margin: auto;
	}
	@media screen and (min-width: 20em) {
		.sidefigure {
			float: right;
			width: 50%;
			margin: 0 0 0.5em 0.5em
		}
	}
	.caption, figcaption, caption {
		font-style: italic;
		font-size: 90%;
	}
	.caption::before, figcaption::before, figcaption > .marker {
		font-weight: bold;
	}
	.caption, figcaption {
		counter-increment: figure;
	}

	/* DL list is indented 2em, but figure inside it is not */
	dd > .figure, dd > figure { margin-left: -2em }

/******************************************************************************/
/*                             Colored Boxes                                  */
/******************************************************************************/

	.issue, .note, .example, .assertion, .advisement, blockquote {
		padding: .5em;
		border: .5em;
		border-left-style: solid;
		page-break-inside: avoid;
	}
	span.issue, span.note {
		padding: .1em .5em .15em;
		border-right-style: solid;
	}

	.issue,
	.note,
	.example,
	.advisement,
	.assertion,
	blockquote {
		margin: 1em auto;
	}
	.note  > p:first-child,
	.issue > p:first-child,
	blockquote > :first-child {
		margin-top: 0;
	}
	blockquote > :last-child {
		margin-bottom: 0;
	}

/** Blockquotes ***************************************************************/

	blockquote {
		border-color: silver;
	}

/** Open issue ****************************************************************/

	.issue {
		border-color: #E05252;
		background: #FBE9E9;
		counter-increment: issue;
		overflow: auto;
	}
	.issue::before, .issue > .marker {
		text-transform: uppercase;
		color: #AE1E1E;
		padding-right: 1em;
		text-transform: uppercase;
	}
	/* Add .issue::before { content: "Issue " counter(issue) " "; } for autogen numbers,
	   or use class="marker" to mark up the issue number in source. */

/** Example *******************************************************************/

	.example {
		border-color: #E0CB52;
		background: #FCFAEE;
		counter-increment: example;
		overflow: auto;
		clear: both;
	}
	.example::before, .example > .marker {
		text-transform: uppercase;
		color: #827017;
		min-width: 7.5em;
		display: block;
	}
	/* Add .example::before { content: "Example " counter(example) " "; } for autogen numbers,
	   or use class="marker" to mark up the example number in source. */

/** Non-normative Note ********************************************************/

	.note {
		border-color: #52E052;
		background: #E9FBE9;
		overflow: auto;
	}

	.note::before, .note > .marker,
	details.note > summary::before,
	details.note > summary > .marker {
		text-transform: uppercase;
		display: block;
		color: hsl(120, 70%, 30%);
	}
	/* Add .note::before { content: "Note"; } for autogen label,
	   or use class="marker" to mark up the label in source. */

	details.note > summary {
		display: block;
		color: hsl(120, 70%, 30%);
	}
	details.note[open] > summary {
		border-bottom: 1px silver solid;
	}

/** Assertion Box *************************************************************/
	/*  for assertions in algorithms */

	.assertion {
		border-color: #AAA;
		background: #EEE;
	}

/** Advisement Box ************************************************************/
	/*  for attention-grabbing normative statements */

	.advisement {
		border-color: orange;
		border-style: none solid;
		background: #FFEECC;
	}
	strong.advisement {
		display: block;
		text-align: center;
	}
	.advisement > .marker {
		color: #B35F00;
	}

/** Spec Obsoletion Notice ****************************************************/
	/* obnoxious obsoletion notice for older/abandoned specs. */

	details {
		display: block;
	}
	summary {
		font-weight: bolder;
	}

	.annoying-warning:not(details),
	details.annoying-warning:not([open]) > summary,
	details.annoying-warning[open] {
		background: #fdd;
		color: red;
		font-weight: bold;
		padding: .75em 1em;
		border: thick red;
		border-style: solid;
		border-radius: 1em;
	}
	.annoying-warning :last-child {
		margin-bottom: 0;
	}

@media not print {
	details.annoying-warning[open] {
		position: fixed;
		left: 1em;
		right: 1em;
		bottom: 1em;
		z-index: 1000;
	}
}

	details.annoying-warning:not([open]) > summary {
		text-align: center;
	}

/** Entity Definition Boxes ***************************************************/

	.def {
		padding: .5em 1em;
		background: #DEF;
		margin: 1.2em 0;
		border-left: 0.5em solid #8CCBF2;
	}

/******************************************************************************/
/*                                    Tables                                  */
/******************************************************************************/

	th, td {
		text-align: left;
		text-align: start;
	}

/** Property/Descriptor Definition Tables *************************************/

	table.def {
		/* inherits .def box styling, see above */
		width: 100%;
		border-spacing: 0;
	}

	table.def td,
	table.def th {
		padding: 0.5em;
		vertical-align: baseline;
		border-bottom: 1px solid #bbd7e9;
	}

	table.def > tbody > tr:last-child th,
	table.def > tbody > tr:last-child td {
		border-bottom: 0;
	}

	table.def th {
		font-style: italic;
		font-weight: normal;
		padding-left: 1em;
		width: 3em;
	}

	/* For when values are extra-complex and need formatting for readability */
	table td.pre {
		white-space: pre-wrap;
	}

	/* A footnote at the bottom of a def table */
	table.def           td.footnote {
		padding-top: 0.6em;
	}
	table.def           td.footnote::before {
		content: " ";
		display: block;
		height: 0.6em;
		width: 4em;
		border-top: thin solid;
	}

/** Data tables (and properly marked-up index tables) *************************/
	/*
		 <table class="data"> highlights structural relationships in a table
		 when correct markup is used (e.g. thead/tbody, th vs. td, scope attribute)

		 Use class="complex data" for particularly complicated tables --
		 (This will draw more lines: busier, but clearer.)

		 Use class="long" on table cells with paragraph-like contents
		 (This will adjust text alignment accordingly.)
		 Alternately use class="longlastcol" on tables, to have the last column assume "long".
	*/

	table {
		word-wrap: normal;
		overflow-wrap: normal;
		hyphens: manual;
	}

	table.data,
	table.index {
		margin: 1em auto;
		border-collapse: collapse;
		border: hidden;
		width: 100%;
	}
	table.data caption,
	table.index caption {
		max-width: 50em;
		margin: 0 auto 1em;
	}

	table.data td,  table.data th,
	table.index td, table.index th {
		padding: 0.5em 1em;
		border-width: 1px;
		border-color: silver;
		border-top-style: solid;
	}

	table.data thead td:empty {
		padding: 0;
		border: 0;
	}

	table.data  thead,
	table.index thead,
	table.data  tbody,
	table.index tbody {
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 <body class="h-entry">
  <div class="head">
   <p data-fill-with="logo"></p>
   <h1 class="p-name no-ref" id="title">P0323R6<br>std::expected</h1>
   <h2 class="no-num no-toc no-ref heading settled" id="subtitle"><span class="content">Published Proposal, <time class="dt-updated" datetime="1970-01-01">1970-01-01</time></span></h2>
   <div data-fill-with="spec-metadata">
    <dl>
     <dt>This version:
     <dd><a class="u-url" href="https://wg21.link/P0323r6">https://wg21.link/P0323r6</a>
     <dt>Authors:
     <dd>
      <dd class="editor p-author h-card vcard"><a class="p-name fn u-email email" href="mailto:vicente.botet@nokia.com">Vicente Botet</a> (<span class="p-org org">Nokia</span>)
     <dd>
      <dd class="editor p-author h-card vcard"><a class="p-name fn u-email email" href="mailto:jfbastien@apple.com">JF Bastien</a> (<span class="p-org org">Apple</span>)
     <dt>Audience:
     <dd>LWG
     <dt>Project:
     <dd>ISO/IEC JTC1/SC22/WG21 14882: Programming Language — C++
     <dt>Source:
     <dd><a href="https://github.com/jfbastien/papers/blob/master/source/P0323r6.bs">github.com/jfbastien/papers/blob/master/source/P0323r6.bs</a>
    </dl>
   </div>
   <div data-fill-with="warning"></div>
   <hr title="Separator for header">
  </div>
  <div class="p-summary" data-fill-with="abstract">
   <h2 class="no-num no-toc no-ref heading settled" id="abstract"><span class="content">Abstract</span></h2>
   <p>Utility class to represent expected object: wording and open questions.</p>
  </div>
  <nav data-fill-with="table-of-contents" id="toc">
   <h2 class="no-num no-toc no-ref" id="contents">Table of Contents</h2>
   <ol class="toc" role="directory">
    <li>
     <a href="#word"><span class="secno">1</span> <span class="content">Wording</span></a>
     <ol class="toc">
      <li><a href="#expected"><span class="secno">1.1</span> <span class="content">�.� Expected objects [<em>expected</em>]</span></a>
      <li><a href="#expected.general"><span class="secno">1.2</span> <span class="content">�.�.1 In general [<em>expected.general</em>]</span></a>
      <li><a href="#expected.synop"><span class="secno">1.3</span> <span class="content">�.�.2 Header <code class="highlight"><c- o>&lt;</c-><c- n>experimental</c-><c- o>/</c-><c- n>expected</c-><c- o>></c-></code> synopsis [<em>expected.synop</em>]</span></a>
      <li><a href="#expected.defs"><span class="secno">1.4</span> <span class="content">�.�.3 Definitions [<em>expected.defs</em>]</span></a>
      <li><a href="#expected.expected"><span class="secno">1.5</span> <span class="content">�.�.4 Class template expected [<em>expected.expected</em>]</span></a>
      <li><a href="#expected.object.ctor"><span class="secno">1.6</span> <span class="content">�.�.4.1 Constructors [<em>expected.object.ctor</em>]</span></a>
      <li><a href="#expected.object.dtor"><span class="secno">1.7</span> <span class="content">�.�.4.2 Destructor [<em>expected.object.dtor</em>]</span></a>
      <li><a href="#expected.object.assign"><span class="secno">1.8</span> <span class="content">�.�.4.3 Assignment [<em>expected.object.assign</em>]</span></a>
      <li><a href="#expected.object.swap"><span class="secno">1.9</span> <span class="content">�.�.4.4 Swap [<em>expected.object.swap</em>]</span></a>
      <li><a href="#expected.object.observe"><span class="secno">1.10</span> <span class="content">�.�.4.5 Observers [<em>expected.object.observe</em>]</span></a>
      <li><a href="#expected.equality_op"><span class="secno">1.11</span> <span class="content">�.�.4.6 Expected Equality operators [<em>expected.equality_op</em>]</span></a>
      <li><a href="#expected.comparison_T"><span class="secno">1.12</span> <span class="content">�.�.4.7 Comparison with <code class="highlight"><c- n>T</c-></code> [<em>expected.comparison_T</em>]</span></a>
      <li><a href="#expected.comparison_unexpected_E"><span class="secno">1.13</span> <span class="content">�.�.4.8 Comparison with <code class="highlight"><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code> [<em>expected.comparison_unexpected_E</em>]</span></a>
      <li><a href="#expected.specalg"><span class="secno">1.14</span> <span class="content">�.�.4.9 Specialized algorithms [<em>expected.specalg</em>]</span></a>
      <li><a href="#expected.unexpected"><span class="secno">1.15</span> <span class="content">�.�.5 Unexpected objects [<em>expected.unexpected</em>]</span></a>
      <li><a href="#expected.unexpected.general"><span class="secno">1.16</span> <span class="content">�.�.5.1 General [<em>expected.unexpected.general</em>]</span></a>
      <li><a href="#expected.unexpected.object"><span class="secno">1.17</span> <span class="content">�.�.5.2 Class template <code class="highlight"><c- n>unexpected</c-></code> [<em>expected.unexpected.object</em>]</span></a>
      <li><a href="#expected.unexpected.equality_op"><span class="secno">1.18</span> <span class="content">�.�.5.2.5 Equality operators [<em>expected.unexpected.equality_op</em>]</span></a>
      <li><a href="#expected.bad_expected_access"><span class="secno">1.19</span> <span class="content">�.�.6 Template Class <code class="highlight"><c- n>bad_expected_access</c-></code> [<em>expected.bad_expected_access</em>]</span></a>
      <li><a href="#expected.bad_expected_access_base"><span class="secno">1.20</span> <span class="content">�.�.7 Class <code class="highlight"><c- n>bad_expected_access</c-><c- o>&lt;</c-><c- b>void</c-><c- o>></c-></code> [<em>expected.bad_expected_access_base</em>]</span></a>
      <li><a href="#expected.unexpect"><span class="secno">1.21</span> <span class="content">�.�.8 <code class="highlight"><c- n>unexpect</c-></code> tag [<em>expected.unexpect</em>]</span></a>
     </ol>
    <li>
     <a href="#qq"><span class="secno">2</span> <span class="content">Open Questions</span></a>
     <ol class="toc">
      <li><a href="#ergo"><span class="secno">2.1</span> <span class="content">Ergonomics</span></a>
      <li><a href="#dis"><span class="secno">2.2</span> <span class="content">Disappointment</span></a>
      <li><a href="#stl"><span class="secno">2.3</span> <span class="content">STL Usage</span></a>
     </ol>
    <li>
     <a href="#references"><span class="secno"></span> <span class="content">References</span></a>
     <ol class="toc">
      <li><a href="#informative"><span class="secno"></span> <span class="content">Informative References</span></a>
     </ol>
    <li><a href="#issues-index"><span class="secno"></span> <span class="content">Issues Index</span></a>
   </ol>
  </nav>
  <main>
   <p>This paper revises <a data-link-type="biblio" href="#biblio-p0323r5">[P0323r5]</a>, which applied feedback obtained from LEWG and
EWG.</p>
   <p>r6 takes in account the LWG feedback in Jacksonville.</p>
   <ul>
    <li data-md>
     <p>Locate <code class="highlight"><c- n>unexpected</c-></code> inside <code class="highlight"><c- o>&lt;</c-><c- n>expected</c-><c- o>></c-></code> header and section.</p>
    <li data-md>
     <p>Define friend functions for equality operators and <code class="highlight"><c- n>swap</c-></code>.</p>
    <li data-md>
     <p>Follows as much as possible <code class="highlight"><c- n>variant</c-></code> kind of wording.</p>
    <li data-md>
     <p>Reword <code class="highlight"><c- n>emplace</c-><c- p>(</c-><c- n>initializer_list</c-><c- p>)</c-></code> overload.</p>
    <li data-md>
     <p>Use <code class="highlight"><c- n>trait</c-></code> is <code class="highlight">true</code>/ <code class="highlight">false</code>.</p>
    <li data-md>
     <p>Simplify Effects clause when there is a simple return.</p>
   </ul>
   <p>We have added some additional open points that have not been identified previously after the LWG’s feedback:</p>
   <ul>
    <li data-md>
     <p>Has <code class="highlight"><c- n>unexpected</c-><c- o>&lt;</c-><c- b>void</c-><c- o>></c-></code> a sense?</p>
    <li data-md>
     <p>Missing <code class="highlight"><c- n>expected</c-><c- o>&lt;</c-><c- n>T</c-><c- p>,</c-><c- n>E</c-><c- o>>::</c-><c- n>emplace</c-></code> for <code class="highlight"><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code>.</p>
    <li data-md>
     <p>The in-place construction from a <code class="highlight"><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code> using the <code class="highlight"><c- n>unexpect_t</c-></code> tag doesn’t conveys the in-place nature of this constructor.</p>
   </ul>
   <p>These should be fixed in another paper if LEWG considered the fix necessary.</p>
   <p><a data-link-type="biblio" href="#biblio-p0323r4">[P0323r4]</a> contains motivation, design rationale, implementability information,
sample usage, history, alternative designs and related types. r6 and r5 only
contain wording and open questions because their purpose is twofold:</p>
   <ul>
    <li data-md>
     <p>Present appropriate wording for inclusion in the Library Fundamentals TS v3.</p>
    <li data-md>
     <p>List open questions which the TS should aim to answer.</p>
   </ul>
   <h2 class="heading settled" data-level="1" id="word"><span class="secno">1. </span><span class="content">Wording</span><a class="self-link" href="#word"></a></h2>
   <p>Below, substitute the <code class="highlight">�</code> character with a number or name the editor finds
appropriate for the sub-section.</p>
   <h3 class="heading settled" data-level="1.1" id="expected"><span class="secno">1.1. </span><span class="content">�.� Expected objects [<em>expected</em>]</span><a class="self-link" href="#expected"></a></h3>
   <h3 class="heading settled" data-level="1.2" id="expected.general"><span class="secno">1.2. </span><span class="content">�.�.1 In general [<em>expected.general</em>]</span><a class="self-link" href="#expected.general"></a></h3>
   <p>This subclause describes class template <code class="highlight"><c- n>expected</c-></code> that represents expected
objects. An <code class="highlight"><c- n>expected</c-><c- o>&lt;</c-><c- n>T</c-><c- p>,</c-> <c- n>E</c-><c- o>></c-></code> object holds an object of type <code class="highlight"><c- n>T</c-></code> or an object of
type <code class="highlight"><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code> and manages the lifetime of the contained objects.</p>
   <h3 class="heading settled" data-level="1.3" id="expected.synop"><span class="secno">1.3. </span><span class="content">�.�.2 Header <code class="highlight"><c- o>&lt;</c-><c- n>experimental</c-><c- o>/</c-><c- n>expected</c-><c- o>></c-></code> synopsis [<em>expected.synop</em>]</span><a class="self-link" href="#expected.synop"></a></h3>
<pre class="language-c++ highlight"><c- n>namespace</c-> <c- n>std</c-> <c- p>{</c->
<c- n>namespace</c-> <c- n>experimental</c-> <c- p>{</c->
<c- kr>inline</c-> <c- n>namespace</c-> <c- n>fundamentals_v3</c-> <c- p>{</c->
	<c- c1>// �.�.4, class template expected</c->
    <c- n>template</c-> <c- o>&lt;</c-><c- n>class</c-> <c- n>T</c-><c- p>,</c-> <c- n>class</c-> <c- n>E</c-><c- o>></c->
        <c- n>class</c-> <c- n>expected</c-><c- p>;</c->

    <c- c1>// �.�.5, class template unexpected</c->
    <c- n>template</c-> <c- o>&lt;</c-><c- n>class</c-> <c- n>E</c-><c- o>></c->
        <c- n>class</c-> <c- n>unexpected</c-><c- p>;</c->
	<c- n>template</c-> <c- o>&lt;</c-><c- n>class</c-> <c- n>E</c-><c- o>></c->
	  <c- n>unexpected</c-><c- p>(</c-><c- n>E</c-><c- p>)</c-> <c- o>-></c-> <c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-><c- p>;</c->
	
    <c- c1>// �.�.6, class bad_expected_access</c->
    <c- n>template</c-> <c- o>&lt;</c-><c- n>class</c-> <c- n>E</c-><c- o>></c->
       <c- n>class</c-> <c- n>bad_expected_access</c-><c- p>;</c->

    <c- c1>// �.�.7, Specialization for void</c->
    <c- n>template</c-> <c- o>&lt;></c->
       <c- n>class</c-> <c- n>bad_expected_access</c-><c- o>&lt;</c-><c- b>void</c-><c- o>></c-><c- p>;</c->

    <c- c1>// �.�.8, unexpect tag</c->
    <c- k>struct</c-> <c- n>unexpect_t</c-> <c- p>{</c->
       <c- n>explicit</c-> <c- n>unexpect_t</c-><c- p>()</c-> <c- o>=</c-> <c- k>default</c-><c- p>;</c->
    <c- p>};</c->
    <c- kr>inline</c-> <c- n>constexpr</c-> <c- n>unexpect_t</c-> <c- n>unexpect</c-><c- p>{};</c->

<c- p>}}}</c->
</pre>
   <p>A program that instantiates the definition of <code class="highlight"><c- n>unexpected</c-></code> for a
non-object type, a function type, an array object, an <code class="highlight"><c- n>unexpected</c-><c- o>&lt;</c-><c- n>G</c-><c- o>></c-></code> object type or
an object type cv-qualified is ill-formed.</p>
   <p>A program that instantiates the definition of template <code class="highlight"><c- n>expected</c-><c- o>&lt;</c-><c- n>T</c-><c- p>,</c-> <c- n>E</c-><c- o>></c-></code> for a reference type or for possibly cv-qualified types <code class="highlight"><c- n>in_place_t</c-></code>, <code class="highlight"><c- n>unexpect_t</c-></code> or <code class="highlight"><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code> for the <code class="highlight"><c- n>T</c-></code> parameter or
for a reference type or for possibly cv-qualified <code class="highlight"><c- b>void</c-></code> type for the <code class="highlight"><c- n>E</c-></code> parameter
is ill-formed.</p>
   <h3 class="heading settled" data-level="1.4" id="expected.defs"><span class="secno">1.4. </span><span class="content">�.�.3 Definitions [<em>expected.defs</em>]</span><a class="self-link" href="#expected.defs"></a></h3>
   <p>An instance of <code class="highlight"><c- n>expected</c-><c- o>&lt;</c-><c- n>T</c-><c- p>,</c-> <c- n>E</c-><c- o>></c-></code> is said to be valued if it contains a object of
type <code class="highlight"><c- n>T</c-></code>. An instance of <code class="highlight"><c- n>expected</c-><c- o>&lt;</c-><c- n>T</c-><c- p>,</c-> <c- n>E</c-><c- o>></c-></code> is said to be disapointed if it
contains an object of type <code class="highlight"><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code>.</p>
   <h3 class="heading settled" data-level="1.5" id="expected.expected"><span class="secno">1.5. </span><span class="content">�.�.4 Class template expected [<em>expected.expected</em>]</span><a class="self-link" href="#expected.expected"></a></h3>
<pre class="language-c++ highlight"><c- n>template</c-> <c- o>&lt;</c-><c- n>class</c-> <c- n>T</c-><c- p>,</c-> <c- n>class</c-> <c- n>E</c-><c- o>></c->
<c- n>class</c-> <c- n>expected</c-> <c- p>{</c->
<c- nl>public</c-><c- p>:</c->
    <c- n>using</c-> <c- n>value_type</c-> <c- o>=</c-> <c- n>T</c-><c- p>;</c->
    <c- n>using</c-> <c- n>error_type</c-> <c- o>=</c-> <c- n>E</c-><c- p>;</c->
    <c- n>using</c-> <c- n>unexpected_type</c-> <c- o>=</c-> <c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-><c- p>;</c->

    <c- n>template</c-> <c- o>&lt;</c-><c- n>class</c-> <c- n>U</c-><c- o>></c->
    <c- n>using</c-> <c- n>rebind</c-> <c- o>=</c-> <c- n>expected</c-><c- o>&lt;</c-><c- n>U</c-><c- p>,</c-> <c- n>error_type</c-><c- o>></c-><c- p>;</c->

    <c- c1>// �.�.4.1, constructors</c->
    <c- n>constexpr</c-> <c- nf>expected</c-><c- p>();</c->
    <c- n>constexpr</c-> <c- nf>expected</c-><c- p>(</c-><c- k>const</c-> <c- n>expected</c-><c- o>&amp;</c-><c- p>);</c->
    <c- n>constexpr</c-> <c- nf>expected</c-><c- p>(</c-><c- n>expected</c-><c- o>&amp;&amp;</c-><c- p>)</c-> <c- n>noexcept</c-><c- p>(</c-><c- n>see</c-> <c- n>below</c-><c- p>);</c->
    <c- n>template</c-> <c- o>&lt;</c-><c- n>class</c-> <c- n>U</c-><c- p>,</c-> <c- n>class</c-> <c- n>G</c-><c- o>></c->
        <c- n>EXPLICIT</c-> <c- n>constexpr</c-> <c- n>expected</c-><c- p>(</c-><c- k>const</c-> <c- n>expected</c-><c- o>&lt;</c-><c- n>U</c-><c- p>,</c-> <c- n>G</c-><c- o>>&amp;</c-><c- p>);</c->
    <c- n>template</c-> <c- o>&lt;</c-><c- n>class</c-> <c- n>U</c-><c- p>,</c-> <c- n>class</c-> <c- n>G</c-><c- o>></c->
        <c- n>EXPLICIT</c-> <c- n>constexpr</c-> <c- n>expected</c-><c- p>(</c-><c- n>expected</c-><c- o>&lt;</c-><c- n>U</c-><c- p>,</c-> <c- n>G</c-><c- o>>&amp;&amp;</c-><c- p>);</c->

    <c- n>template</c-> <c- o>&lt;</c-><c- n>class</c-> <c- n>U</c-> <c- o>=</c-> <c- n>T</c-><c- o>></c->
        <c- n>EXPLICIT</c-> <c- n>constexpr</c-> <c- n>expected</c-><c- p>(</c-><c- n>U</c-><c- o>&amp;&amp;</c-> <c- n>v</c-><c- p>);</c->

    <c- n>template</c-> <c- o>&lt;</c-><c- n>class</c-> <c- n>G</c-> <c- o>=</c-> <c- n>E</c-><c- o>></c->
        <c- n>constexpr</c-> <c- n>expected</c-><c- p>(</c-><c- k>const</c-> <c- n>unexpected</c-><c- o>&lt;</c-><c- n>G</c-><c- o>>&amp;</c-><c- p>);</c->
    <c- n>template</c-> <c- o>&lt;</c-><c- n>class</c-> <c- n>G</c-> <c- o>=</c-> <c- n>E</c-><c- o>></c->
        <c- n>constexpr</c-> <c- n>expected</c-><c- p>(</c-><c- n>unexpected</c-><c- o>&lt;</c-><c- n>G</c-><c- o>></c-> <c- o>&amp;&amp;</c-><c- p>);</c->

	<c- n>template</c-> <c- o>&lt;</c-><c- n>class</c-><c- p>...</c-> <c- n>Args</c-><c- o>></c->
        <c- n>constexpr</c-> <c- n>explicit</c-> <c- n>expected</c-><c- p>(</c-><c- n>in_place_t</c-><c- p>,</c-> <c- n>Args</c-><c- o>&amp;&amp;</c-><c- p>...);</c->
    <c- n>template</c-> <c- o>&lt;</c-><c- n>class</c-> <c- n>U</c-><c- p>,</c-> <c- n>class</c-><c- p>...</c-> <c- n>Args</c-><c- o>></c->
        <c- n>constexpr</c-> <c- n>explicit</c-> <c- n>expected</c-><c- p>(</c-><c- n>in_place_t</c-><c- p>,</c-> <c- n>initializer_list</c-><c- o>&lt;</c-><c- n>U</c-><c- o>></c-><c- p>,</c-> <c- n>Args</c-><c- o>&amp;&amp;</c-><c- p>...);</c->
    <c- n>template</c-> <c- o>&lt;</c-><c- n>class</c-><c- p>...</c-> <c- n>Args</c-><c- o>></c->
        <c- n>constexpr</c-> <c- n>explicit</c-> <c- n>expected</c-><c- p>(</c-><c- n>unexpect_t</c-><c- p>,</c-> <c- n>Args</c-><c- o>&amp;&amp;</c-><c- p>...);</c->
    <c- n>template</c-> <c- o>&lt;</c-><c- n>class</c-> <c- n>U</c-><c- p>,</c-> <c- n>class</c-><c- p>...</c-> <c- n>Args</c-><c- o>></c->
        <c- n>constexpr</c-> <c- n>explicit</c-> <c- n>expected</c-><c- p>(</c-><c- n>unexpect_t</c-><c- p>,</c-> <c- n>initializer_list</c-><c- o>&lt;</c-><c- n>U</c-><c- o>></c-><c- p>,</c-> <c- n>Args</c-><c- o>&amp;&amp;</c-><c- p>...);</c->

		
    <c- c1>// �.�.4.2, destructor</c->
    <c- o>~</c-><c- n>expected</c-><c- p>();</c->

    <c- c1>// �.�.4.3, assignment</c->
    <c- n>expected</c-><c- o>&amp;</c-> <c- n>operator</c-><c- o>=</c-><c- p>(</c-><c- k>const</c-> <c- n>expected</c-><c- o>&amp;</c-><c- p>);</c->
    <c- n>expected</c-><c- o>&amp;</c-> <c- n>operator</c-><c- o>=</c-><c- p>(</c-><c- n>expected</c-><c- o>&amp;&amp;</c-><c- p>)</c-> <c- n>noexcept</c-><c- p>(</c-><c- n>see</c-> <c- n>below</c-><c- p>);</c->
    <c- n>template</c-> <c- o>&lt;</c-><c- n>class</c-> <c- n>U</c-> <c- o>=</c-> <c- n>T</c-><c- o>></c-> <c- n>expected</c-><c- o>&amp;</c-> <c- n>operator</c-><c- o>=</c-><c- p>(</c-><c- n>U</c-><c- o>&amp;&amp;</c-><c- p>);</c->
    <c- n>template</c-> <c- o>&lt;</c-><c- n>class</c-> <c- n>G</c-> <c- o>=</c-> <c- n>E</c-><c- o>></c->
        <c- n>expected</c-><c- o>&amp;</c-> <c- n>operator</c-><c- o>=</c-><c- p>(</c-><c- k>const</c-> <c- n>unexpected</c-><c- o>&lt;</c-><c- n>G</c-><c- o>>&amp;</c-><c- p>);</c->
    <c- n>template</c-> <c- o>&lt;</c-><c- n>class</c-> <c- n>G</c-> <c- o>=</c-> <c- n>E</c-><c- o>></c->
        <c- n>expected</c-><c- o>&amp;</c-> <c- n>operator</c-><c- o>=</c-><c- p>(</c-><c- n>unexpected</c-><c- o>&lt;</c-><c- n>G</c-><c- o>>&amp;&amp;</c-><c- p>);</c->

	<c- c1>// �.�.4.4, modifiers</c->

    <c- n>template</c-> <c- o>&lt;</c-><c- n>class</c-><c- p>...</c-> <c- n>Args</c-><c- o>></c->
        <c- n>T</c-><c- o>&amp;</c-> <c- n>emplace</c-><c- p>(</c-><c- n>Args</c-><c- o>&amp;&amp;</c-><c- p>...);</c->
    <c- n>template</c-> <c- o>&lt;</c-><c- n>class</c-> <c- n>U</c-><c- p>,</c-> <c- n>class</c-><c- p>...</c-> <c- n>Args</c-><c- o>></c->
        <c- n>T</c-><c- o>&amp;</c-> <c- n>emplace</c-><c- p>(</c-><c- n>initializer_list</c-><c- o>&lt;</c-><c- n>U</c-><c- o>></c-><c- p>,</c-> <c- n>Args</c-><c- o>&amp;&amp;</c-><c- p>...);</c->
		
    <c- c1>// �.�.4.5, swap</c->
    <c- b>void</c-> <c- nf>swap</c-><c- p>(</c-><c- n>expected</c-><c- o>&amp;</c-><c- p>)</c-> <c- n>noexcept</c-><c- p>(</c-><c- n>see</c-> <c- n>below</c-><c- p>);</c->

    <c- c1>// �.�.4.6, observers</c->
    <c- n>constexpr</c-> <c- k>const</c-> <c- n>T</c-><c- o>*</c-> <c- n>operator</c-> <c- o>-></c-><c- p>()</c-> <c- k>const</c-><c- p>;</c->
    <c- n>constexpr</c-> <c- n>T</c-><c- o>*</c-> <c- n>operator</c-> <c- o>-></c-><c- p>();</c->
    <c- n>constexpr</c-> <c- k>const</c-> <c- n>T</c-><c- o>&amp;</c-> <c- n>operator</c-> <c- o>*</c-><c- p>()</c-> <c- k>const</c-><c- o>&amp;</c-><c- p>;</c->
    <c- n>constexpr</c-> <c- n>T</c-><c- o>&amp;</c-> <c- n>operator</c-> <c- o>*</c-><c- p>()</c-> <c- o>&amp;</c-><c- p>;</c->
    <c- n>constexpr</c-> <c- k>const</c-> <c- n>T</c-><c- o>&amp;&amp;</c-> <c- n>operator</c-> <c- o>*</c-><c- p>()</c-> <c- k>const</c-> <c- o>&amp;&amp;</c-><c- p>;</c->
    <c- n>constexpr</c-> <c- n>T</c-><c- o>&amp;&amp;</c-> <c- n>operator</c-> <c- o>*</c-><c- p>()</c-> <c- o>&amp;&amp;</c-><c- p>;</c->
    <c- n>constexpr</c-> <c- n>explicit</c-> <c- n>operator</c-> <c- nf>bool</c-><c- p>()</c-> <c- k>const</c-> <c- n>noexcept</c-><c- p>;</c->
    <c- n>constexpr</c-> <c- b>bool</c-> <c- nf>has_value</c-><c- p>()</c-> <c- k>const</c-> <c- n>noexcept</c-><c- p>;</c->
    <c- n>constexpr</c-> <c- k>const</c-> <c- n>T</c-><c- o>&amp;</c-> <c- n>value</c-><c- p>()</c-> <c- k>const</c-><c- o>&amp;</c-><c- p>;</c->
    <c- n>constexpr</c-> <c- n>T</c-><c- o>&amp;</c-> <c- n>value</c-><c- p>()</c-> <c- o>&amp;</c-><c- p>;</c->
    <c- n>constexpr</c-> <c- k>const</c-> <c- n>T</c-><c- o>&amp;&amp;</c-> <c- n>value</c-><c- p>()</c-> <c- k>const</c-> <c- o>&amp;&amp;</c-><c- p>;</c->
    <c- n>constexpr</c-> <c- n>T</c-><c- o>&amp;&amp;</c-> <c- n>value</c-><c- p>()</c-> <c- o>&amp;&amp;</c-><c- p>;</c->
    <c- n>constexpr</c-> <c- k>const</c-> <c- n>E</c-><c- o>&amp;</c-> <c- n>error</c-><c- p>()</c-> <c- k>const</c-><c- o>&amp;</c-><c- p>;</c->
    <c- n>constexpr</c-> <c- n>E</c-><c- o>&amp;</c-> <c- n>error</c-><c- p>()</c-> <c- o>&amp;</c-><c- p>;</c->
    <c- n>constexpr</c-> <c- k>const</c-> <c- n>E</c-><c- o>&amp;&amp;</c-> <c- n>error</c-><c- p>()</c-> <c- k>const</c-> <c- o>&amp;&amp;</c-><c- p>;</c->
    <c- n>constexpr</c-> <c- n>E</c-><c- o>&amp;&amp;</c-> <c- n>error</c-><c- p>()</c-> <c- o>&amp;&amp;</c-><c- p>;</c->
    <c- n>template</c-> <c- o>&lt;</c-><c- n>class</c-> <c- n>U</c-><c- o>></c->
        <c- n>constexpr</c-> <c- n>T</c-> <c- n>value_or</c-><c- p>(</c-><c- n>U</c-><c- o>&amp;&amp;</c-><c- p>)</c-> <c- k>const</c-><c- o>&amp;</c-><c- p>;</c->
    <c- n>template</c-> <c- o>&lt;</c-><c- n>class</c-> <c- n>U</c-><c- o>></c->
        <c- n>constexpr</c-> <c- n>T</c-> <c- n>value_or</c-><c- p>(</c-><c- n>U</c-><c- o>&amp;&amp;</c-><c- p>)</c-> <c- o>&amp;&amp;</c-><c- p>;</c->
		
    <c- c1>// �.�.4.7, Expected equality operators</c->
    <c- n>template</c-> <c- o>&lt;</c-><c- n>class</c-> <c- n>T1</c-><c- p>,</c-> <c- n>class</c-> <c- n>E1</c-><c- p>,</c-> <c- n>class</c-> <c- n>T2</c-><c- p>,</c-> <c- n>class</c-> <c- n>E2</c-><c- o>></c->
        <c- n>friend</c-> <c- n>constexpr</c-> <c- b>bool</c-> <c- n>operator</c-><c- o>==</c-><c- p>(</c-><c- k>const</c-> <c- n>expected</c-><c- o>&lt;</c-><c- n>T1</c-><c- p>,</c-> <c- n>E1</c-><c- o>>&amp;</c-> <c- n>x</c-><c- p>,</c-> <c- k>const</c-> <c- n>expected</c-><c- o>&lt;</c-><c- n>T2</c-><c- p>,</c-> <c- n>E2</c-><c- o>>&amp;</c-> <c- n>y</c-><c- p>);</c->
    <c- n>template</c-> <c- o>&lt;</c-><c- n>class</c-> <c- n>T1</c-><c- p>,</c-> <c- n>class</c-> <c- n>E1</c-><c- p>,</c-> <c- n>class</c-> <c- n>T2</c-><c- p>,</c-> <c- n>class</c-> <c- n>E2</c-><c- o>></c->
        <c- n>friend</c-> <c- n>constexpr</c-> <c- b>bool</c-> <c- n>operator</c-><c- o>!=</c-><c- p>(</c-><c- k>const</c-> <c- n>expected</c-><c- o>&lt;</c-><c- n>T1</c-><c- p>,</c-> <c- n>E1</c-><c- o>>&amp;</c-> <c- n>x</c-><c- p>,</c-> <c- k>const</c-> <c- n>expected</c-><c- o>&lt;</c-><c- n>T2</c-><c- p>,</c-> <c- n>E2</c-><c- o>>&amp;</c-> <c- n>y</c-><c- p>);</c->

    <c- c1>// �.�.4.8, Comparison with T</c->
    <c- n>template</c-> <c- o>&lt;</c-><c- n>class</c-> <c- n>T1</c-><c- p>,</c-> <c- n>class</c-> <c- n>E1</c-><c- p>,</c-> <c- n>class</c-> <c- n>T2</c-><c- o>></c->
		<c- n>friend</c-> <c- n>constexpr</c-> <c- b>bool</c-> <c- n>operator</c-><c- o>==</c-><c- p>(</c-><c- k>const</c-> <c- n>expected</c-><c- o>&lt;</c-><c- n>T1</c-><c- p>,</c-> <c- n>E1</c-><c- o>>&amp;</c-><c- p>,</c-> <c- k>const</c-> <c- n>T2</c-><c- o>&amp;</c-><c- p>);</c->
    <c- n>template</c-> <c- o>&lt;</c-><c- n>class</c-> <c- n>T1</c-><c- p>,</c-> <c- n>class</c-> <c- n>E1</c-><c- p>,</c-> <c- n>class</c-> <c- n>T2</c-><c- o>></c->
		<c- n>friend</c-> <c- n>constexpr</c-> <c- b>bool</c-> <c- n>operator</c-><c- o>==</c-><c- p>(</c-><c- k>const</c-> <c- n>T2</c-><c- o>&amp;</c-><c- p>,</c-> <c- k>const</c-> <c- n>expected</c-><c- o>&lt;</c-><c- n>T1</c-><c- p>,</c-> <c- n>E1</c-><c- o>>&amp;</c-><c- p>);</c->
    <c- n>template</c-> <c- o>&lt;</c-><c- n>class</c-> <c- n>T1</c-><c- p>,</c-> <c- n>class</c-> <c- n>E1</c-><c- p>,</c-> <c- n>class</c-> <c- n>T2</c-><c- o>></c->
		<c- n>friend</c-> <c- n>constexpr</c-> <c- b>bool</c-> <c- n>operator</c-><c- o>!=</c-><c- p>(</c-><c- k>const</c-> <c- n>expected</c-><c- o>&lt;</c-><c- n>T1</c-><c- p>,</c-> <c- n>E1</c-><c- o>>&amp;</c-><c- p>,</c-> <c- k>const</c-> <c- n>T2</c-><c- o>&amp;</c-><c- p>);</c->
    <c- n>template</c-> <c- o>&lt;</c-><c- n>class</c-> <c- n>T1</c-><c- p>,</c-> <c- n>class</c-> <c- n>E1</c-><c- p>,</c-> <c- n>class</c-> <c- n>T2</c-><c- o>></c->
		<c- n>friend</c-> <c- n>constexpr</c-> <c- b>bool</c-> <c- n>operator</c-><c- o>!=</c-><c- p>(</c-><c- k>const</c-> <c- n>T2</c-><c- o>&amp;</c-><c- p>,</c-> <c- k>const</c-> <c- n>expected</c-><c- o>&lt;</c-><c- n>T1</c-><c- p>,</c-> <c- n>E1</c-><c- o>>&amp;</c-><c- p>);</c->

    <c- c1>// �.�.4.9, Comparison with unexpected&lt;E></c->
    <c- n>template</c-> <c- o>&lt;</c-><c- n>class</c-> <c- n>T1</c-><c- p>,</c-> <c- n>class</c-> <c- n>E1</c-><c- p>,</c-> <c- n>class</c-> <c- n>E2</c-><c- o>></c->
		<c- n>friend</c-> <c- n>constexpr</c-> <c- b>bool</c-> <c- n>operator</c-><c- o>==</c-><c- p>(</c-><c- k>const</c-> <c- n>expected</c-><c- o>&lt;</c-><c- n>T1</c-><c- p>,</c-> <c- n>E1</c-><c- o>>&amp;</c-><c- p>,</c-> <c- k>const</c-> <c- n>unexpected</c-><c- o>&lt;</c-><c- n>E2</c-><c- o>>&amp;</c-><c- p>);</c->
    <c- n>template</c-> <c- o>&lt;</c-><c- n>class</c-> <c- n>T1</c-><c- p>,</c-> <c- n>class</c-> <c- n>E1</c-><c- p>,</c-> <c- n>class</c-> <c- n>E2</c-><c- o>></c->
		<c- n>friend</c-> <c- n>constexpr</c-> <c- b>bool</c-> <c- n>operator</c-><c- o>==</c-><c- p>(</c-><c- k>const</c-> <c- n>unexpected</c-><c- o>&lt;</c-><c- n>E2</c-><c- o>>&amp;</c-><c- p>,</c-> <c- k>const</c-> <c- n>expected</c-><c- o>&lt;</c-><c- n>T1</c-><c- p>,</c-> <c- n>E1</c-><c- o>>&amp;</c-><c- p>);</c->
    <c- n>template</c-> <c- o>&lt;</c-><c- n>class</c-> <c- n>T1</c-><c- p>,</c-> <c- n>class</c-> <c- n>E1</c-><c- p>,</c-> <c- n>class</c-> <c- n>E2</c-><c- o>></c->
		<c- n>friend</c-> <c- n>constexpr</c-> <c- b>bool</c-> <c- n>operator</c-><c- o>!=</c-><c- p>(</c-><c- k>const</c-> <c- n>expected</c-><c- o>&lt;</c-><c- n>T1</c-><c- p>,</c-> <c- n>E1</c-><c- o>>&amp;</c-><c- p>,</c-> <c- k>const</c-> <c- n>unexpected</c-><c- o>&lt;</c-><c- n>E2</c-><c- o>>&amp;</c-><c- p>);</c->
    <c- n>template</c-> <c- o>&lt;</c-><c- n>class</c-> <c- n>T1</c-><c- p>,</c-> <c- n>class</c-> <c- n>E1</c-><c- p>,</c-> <c- n>class</c-> <c- n>E2</c-><c- o>></c->
		<c- n>friend</c-> <c- n>constexpr</c-> <c- b>bool</c-> <c- n>operator</c-><c- o>!=</c-><c- p>(</c-><c- k>const</c-> <c- n>unexpected</c-><c- o>&lt;</c-><c- n>E2</c-><c- o>>&amp;</c-><c- p>,</c-> <c- k>const</c-> <c- n>expected</c-><c- o>&lt;</c-><c- n>T1</c-><c- p>,</c-> <c- n>E1</c-><c- o>>&amp;</c-><c- p>);</c->

    <c- c1>// �.�.4.10, Specialized algorithms</c->
    <c- n>template</c-> <c- o>&lt;</c-><c- n>class</c-> <c- n>T1</c-><c- p>,</c-> <c- n>class</c-> <c- n>E1</c-><c- o>></c->
		<c- n>friend</c-> <c- b>void</c-> <c- n>swap</c-><c- p>(</c-><c- n>expected</c-><c- o>&lt;</c-><c- n>T1</c-><c- p>,</c-> <c- n>E1</c-><c- o>>&amp;</c-><c- p>,</c-> <c- n>expected</c-><c- o>&lt;</c-><c- n>T1</c-><c- p>,</c-> <c- n>E1</c-><c- o>>&amp;</c-><c- p>)</c-> <c- n>noexcept</c-><c- p>(</c-><c- n>see</c-> <c- n>below</c-><c- p>);</c->		

<c- nl>private</c-><c- p>:</c->
    <c- b>bool</c-> <c- n>has_val</c-><c- p>;</c-> <c- c1>// exposition only</c->
    <c- k>union</c->
    <c- p>{</c->
        <c- n>value_type</c-> <c- n>val</c-><c- p>;</c-> <c- c1>// exposition only</c->
        <c- n>unexpected_type</c-> <c- n>unexpect</c-><c- p>;</c-> <c- c1>// exposition only</c->
    <c- p>};</c->
<c- p>};</c->
</pre>
   <p>Any instance of <code class="highlight"><c- n>expected</c-><c- o>&lt;</c-><c- n>T</c-><c- p>,</c-> <c- n>E</c-><c- o>></c-></code> at any given time either contains a value of
type <code class="highlight"><c- n>T</c-></code> or a value of type <code class="highlight"><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code> within their own storage.
Implementations are not permitted to use additional storage, such as dynamic
memory, to allocate the object of type <code class="highlight"><c- n>T</c-></code> or the object of type <code class="highlight"><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code>.
These objects shall be allocated in a region of the <code class="highlight"><c- n>expected</c-><c- o>&lt;</c-><c- n>T</c-><c- p>,</c-> <c- n>E</c-><c- o>></c-></code> storage
suitably aligned for the types <code class="highlight"><c- n>T</c-></code> and <code class="highlight"><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code>. Members <code class="highlight"><c- n>has_val</c-></code>, <code class="highlight"><c- n>val</c-></code> and <code class="highlight"><c- n>unexpect</c-></code> are provided for exposition only. <code class="highlight"><c- n>has_val</c-></code> indicates whether the <code class="highlight"><c- n>expected</c-><c- o>&lt;</c-><c- n>T</c-><c- p>,</c-> <c- n>E</c-><c- o>></c-></code> object is valued.</p>
   <p><code class="highlight"><c- n>T</c-></code> shall be <code class="highlight"><c- b>void</c-></code> or shall be an object type that is not array and shall satisfy the requirements
of <code class="highlight"><c- n>Destructible</c-></code> (Table 27).</p>
   <p><code class="highlight"><c- n>E</c-></code> shall be object type that is not array and shall satisfy the requirements of <code class="highlight"><c- n>Destructible</c-></code> (Table 27).</p>
   <h3 class="heading settled" data-level="1.6" id="expected.object.ctor"><span class="secno">1.6. </span><span class="content">�.�.4.1 Constructors [<em>expected.object.ctor</em>]</span><a class="self-link" href="#expected.object.ctor"></a></h3>
<pre class="language-c++ highlight"><c- n>constexpr</c-> <c- nf>expected</c-><c- p>();</c->
</pre>
   <p><em>Effects</em>: Value-Initializes <code class="highlight"><c- n>val</c-></code> if <code class="highlight"><c- n>T</c-></code> is not <code class="highlight"><c- b>void</c-></code>.</p>
   <p><em>Postconditions</em>: <code class="highlight"><c- b>bool</c-><c- p>(</c-><c- o>*</c-><c- k>this</c-><c- p>)</c-></code>.</p>
   <p><em>Throws</em>: Any exception thrown by the selected constructor of <code class="highlight"><c- n>T</c-></code>.</p>
   <p><em>Remarks</em>: If value-initialization of <code class="highlight"><c- n>T</c-></code> is a constexpr constructor or <code class="highlight"><c- n>T</c-></code> is <code class="highlight"><c- b>void</c-></code> this constructor shall be constexpr. This constructor shall not participate in
overload resolution unless <code class="highlight"><c- n>is_default_constructible_v</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-></code> is <code class="highlight">true</code> or <code class="highlight"><c- n>T</c-></code> is <code class="highlight"><c- b>void</c-></code>.</p>
<pre class="language-c++ highlight"><c- n>constexpr</c-> <c- nf>expected</c-><c- p>(</c-><c- k>const</c-> <c- n>expected</c-><c- o>&amp;</c-> <c- n>rhs</c-><c- p>);</c->
</pre>
   <p><em>Effects</em>: If <code class="highlight"><c- b>bool</c-><c- p>(</c-><c- n>rhs</c-><c- p>)</c-></code>, initializes <code class="highlight"><c- n>val</c-></code> as if
direct-non-list-initializing an object of type <code class="highlight"><c- n>T</c-></code> with the expression <code class="highlight"><c- o>*</c-><c- n>rhs</c-></code> if <code class="highlight"><c- n>T</c-></code> is not <code class="highlight"><c- b>void</c-></code>.</p>
   <p>If <code class="highlight"><c- o>!</c-><c- b>bool</c-><c- p>(</c-><c- n>rhs</c-><c- p>)</c-></code>, initializes <code class="highlight"><c- n>unexpect</c-></code> as if
direct-non-list-initializing an object of type <code class="highlight"><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code> with the
expression <code class="highlight"><c- n>unexpected</c-><c- p>(</c-><c- n>rhs</c-><c- p>.</c-><c- n>error</c-><c- p>())</c-></code>.</p>
   <p><em>Postconditions</em>: <code class="highlight"><c- b>bool</c-><c- p>(</c-><c- n>rhs</c-><c- p>)</c-> <c- o>==</c-> <c- b>bool</c-><c- p>(</c-><c- o>*</c-><c- k>this</c-><c- p>)</c-></code>.</p>
   <p><em>Throws</em>: Any exception thrown by the selected constructors of <code class="highlight"><c- n>T</c-></code> or <code class="highlight"><c- n>E</c-></code>.</p>
   <p><em>Remarks</em>: This constructor shall be defined as deleted unless <code class="highlight"><c- n>is_copy_constructible_v</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-></code> is <code class="highlight">true</code> or <code class="highlight"><c- n>T</c-></code> is <code class="highlight"><c- b>void</c-></code> and <code class="highlight"><c- n>is_copy_constructible_v</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code> is <code class="highlight">true</code>. If <code class="highlight"><c- n>is_trivially_copy_constructible_v</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-></code> is <code class="highlight">true</code> or <code class="highlight"><c- n>T</c-></code> is <code class="highlight"><c- b>void</c-></code> and <code class="highlight"><c- n>is_trivially_copy_constructible_v</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code> is <code class="highlight">true</code>,
this constructor shall be a constexpr constructor.</p>
<pre class="language-c++ highlight"><c- n>constexpr</c-> <c- nf>expected</c-><c- p>(</c-><c- n>expected</c-> <c- o>&amp;&amp;</c-> <c- n>rhs</c-><c- p>)</c-> <c- n>noexcept</c-><c- p>(</c-><c- n>see</c-> <c- n>below</c-><c- p>);</c->
</pre>
   <p><em>Effects</em>: If <code class="highlight"><c- b>bool</c-><c- p>(</c-><c- n>rhs</c-><c- p>)</c-></code>, initializes <code class="highlight"><c- n>val</c-></code> as if
direct-non-list-initializing an object of type <code class="highlight"><c- n>T</c-></code> with the expression <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>move</c-><c- p>(</c-><c- o>*</c-><c- n>rhs</c-><c- p>)</c-></code> (if <code class="highlight"><c- n>T</c-></code> is not <code class="highlight"><c- b>void</c-></code>).</p>
   <p>If <code class="highlight"><c- o>!</c-><c- b>bool</c-><c- p>(</c-><c- n>rhs</c-><c- p>)</c-></code>, initializes <code class="highlight"><c- n>val</c-></code> as if
direct-non-list-initializing an object of type <code class="highlight"><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code> with the
expression <code class="highlight"><c- n>unexpected</c-><c- p>(</c-><c- n>std</c-><c- o>::</c-><c- n>move</c-><c- p>(</c-><c- n>rhs</c-><c- p>.</c-><c- n>error</c-><c- p>()))</c-></code>.</p>
   <p><code class="highlight"><c- b>bool</c-><c- p>(</c-><c- n>rhs</c-><c- p>)</c-></code> is unchanged.</p>
   <p><em>Postconditions</em>: <code class="highlight"><c- b>bool</c-><c- p>(</c-><c- n>rhs</c-><c- p>)</c-> <c- o>==</c-> <c- b>bool</c-><c- p>(</c-><c- o>*</c-><c- k>this</c-><c- p>)</c-></code>.</p>
   <p><em>Throws</em>: Any exception thrown by the selected constructor of <code class="highlight"><c- n>T</c-></code> or <code class="highlight"><c- n>E</c-></code>.</p>
   <p><em>Remarks</em>: The expression inside <code class="highlight"><c- k>noexcept</c-></code> is equivalent to: <code class="highlight"><c- n>is_nothrow_move_constructible_v</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-></code> is <code class="highlight">true</code> or <code class="highlight"><c- n>T</c-></code>is <code class="highlight"><c- b>void</c-></code> and <code class="highlight"><c- n>is_nothrow_move_constructible_v</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code> is <code class="highlight">true</code>. This constructor shall not participate in
overload resolution unless <code class="highlight"><c- n>is_move_constructible_v</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-></code> is <code class="highlight">true</code> and <code class="highlight"><c- n>is_move_constructible_v</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code> is <code class="highlight">true</code>. If <code class="highlight"><c- n>is_trivially_move_constructible_v</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-></code> is <code class="highlight">true</code> or <code class="highlight"><c- n>T</c-></code> is <code class="highlight"><c- b>void</c-></code> and <code class="highlight"><c- n>is_trivially_move_constructible_v</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code> is <code class="highlight">true</code>,
this constructor shall be a constexpr constructor.</p>
<pre class="language-c++ highlight">    <c- n>template</c-> <c- o>&lt;</c-><c- n>class</c-> <c- n>U</c-><c- p>,</c-> <c- n>class</c-> <c- n>G</c-><c- o>></c->
    <c- n>EXPLICIT</c-> <c- n>constexpr</c-> <c- n>expected</c-><c- p>(</c-><c- k>const</c-> <c- n>expected</c-><c- o>&lt;</c-><c- n>U</c-><c- p>,</c-> <c- n>G</c-><c- o>>&amp;</c-> <c- n>rhs</c-><c- p>);</c->
</pre>
   <p><em>Effects</em>: If <code class="highlight"><c- b>bool</c-><c- p>(</c-><c- n>rhs</c-><c- p>)</c-></code>, initializes <code class="highlight"><c- n>val</c-></code> as if
direct-non-list-initializing an object of type <code class="highlight"><c- n>T</c-></code> with the expression <code class="highlight"><c- o>*</c-><c- n>rhs</c-></code>,
if <code class="highlight"><c- n>T</c-></code> is not <code class="highlight"><c- b>void</c-></code>.</p>
   <p>If <code class="highlight"><c- o>!</c-><c- b>bool</c-><c- p>(</c-><c- n>rhs</c-><c- p>)</c-></code> initializes <code class="highlight"><c- n>unexpect</c-></code> as if
direct-non-list-initializing an object of type <code class="highlight"><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code> with the
expression <code class="highlight"><c- n>unexpected</c-><c- p>(</c-><c- n>rhs</c-><c- p>.</c-><c- n>error</c-><c- p>())</c-></code>.</p>
   <p><em>Postconditions</em>: <code class="highlight"><c- b>bool</c-><c- p>(</c-><c- n>rhs</c-><c- p>)</c-> <c- o>==</c-> <c- b>bool</c-><c- p>(</c-><c- o>*</c-><c- k>this</c-><c- p>)</c-></code>.</p>
   <p><em>Throws</em>: Any exception thrown by the selected constructor of <code class="highlight"><c- n>T</c-></code> or <code class="highlight"><c- n>E</c-></code>.</p>
   <p><em>Remarks</em>: This constructor shall not participate in overload resolution unless: <code class="highlight"><c- n>T</c-></code> and <code class="highlight"><c- n>U</c-></code> are <code class="highlight"><c- b>void</c-></code> or</p>
   <ul>
    <li data-md>
     <p><code class="highlight"><c- n>is_constructible_v</c-><c- o>&lt;</c-><c- n>T</c-><c- p>,</c-> <c- k>const</c-> <c- n>U</c-><c- o>&amp;></c-></code> is <code class="highlight">true</code> ,</p>
    <li data-md>
     <p><code class="highlight"><c- n>is_constructible_v</c-><c- o>&lt;</c-><c- n>T</c-><c- p>,</c-> <c- n>expected</c-><c- o>&lt;</c-><c- n>U</c-><c- p>,</c-> <c- n>G</c-><c- o>>&amp;></c-></code> is <code class="highlight">false</code>,</p>
    <li data-md>
     <p><code class="highlight"><c- n>is_constructible_v</c-><c- o>&lt;</c-><c- n>T</c-><c- p>,</c-> <c- n>expected</c-><c- o>&lt;</c-><c- n>U</c-><c- p>,</c-> <c- n>G</c-><c- o>>&amp;&amp;></c-></code> is <code class="highlight">false</code>,</p>
    <li data-md>
     <p><code class="highlight"><c- n>is_constructible_v</c-><c- o>&lt;</c-><c- n>T</c-><c- p>,</c-> <c- k>const</c-> <c- n>expected</c-><c- o>&lt;</c-><c- n>U</c-><c- p>,</c-> <c- n>G</c-><c- o>>&amp;></c-></code> is <code class="highlight">false</code>,</p>
    <li data-md>
     <p><code class="highlight"><c- n>is_constructible_v</c-><c- o>&lt;</c-><c- n>T</c-><c- p>,</c-> <c- k>const</c-> <c- n>expected</c-><c- o>&lt;</c-><c- n>U</c-><c- p>,</c-> <c- n>G</c-><c- o>>&amp;&amp;></c-></code> is <code class="highlight">false</code>,</p>
    <li data-md>
     <p><code class="highlight"><c- n>is_convertible_v</c-><c- o>&lt;</c-><c- n>expected</c-><c- o>&lt;</c-><c- n>U</c-><c- p>,</c-> <c- n>G</c-><c- o>>&amp;</c-><c- p>,</c-> <c- n>T</c-><c- o>></c-></code> is <code class="highlight">false</code>,</p>
    <li data-md>
     <p><code class="highlight"><c- n>is_convertible_v</c-><c- o>&lt;</c-><c- n>expected</c-><c- o>&lt;</c-><c- n>U</c-><c- p>,</c-> <c- n>G</c-><c- o>>&amp;&amp;</c-><c- p>,</c-> <c- n>T</c-><c- o>></c-></code> is <code class="highlight">false</code>,</p>
    <li data-md>
     <p><code class="highlight"><c- n>is_convertible_v</c-><c- o>&lt;</c-><c- k>const</c-> <c- n>expected</c-><c- o>&lt;</c-><c- n>U</c-><c- p>,</c-> <c- n>G</c-><c- o>>&amp;</c-><c- p>,</c-> <c- n>T</c-><c- o>></c-></code> is <code class="highlight">false</code> and</p>
    <li data-md>
     <p><code class="highlight"><c- n>is_convertible_v</c-><c- o>&lt;</c-><c- k>const</c-> <c- n>expected</c-><c- o>&lt;</c-><c- n>U</c-><c- p>,</c-> <c- n>G</c-><c- o>>&amp;&amp;</c-><c- p>,</c-> <c- n>T</c-><c- o>></c-></code> is <code class="highlight">false</code></p>
   </ul>
   <p>and</p>
   <ul>
    <li data-md>
     <p><code class="highlight"><c- n>is_constructible_v</c-><c- o>&lt;</c-><c- n>E</c-><c- p>,</c-> <c- k>const</c-> <c- n>G</c-><c- o>&amp;></c-></code> is <code class="highlight">true</code>,</p>
    <li data-md>
     <p><code class="highlight"><c- n>is_constructible_v</c-><c- o>&lt;</c-><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-><c- p>,</c-> <c- n>expected</c-><c- o>&lt;</c-><c- n>U</c-><c- p>,</c-> <c- n>G</c-><c- o>>&amp;></c-></code> is <code class="highlight">false</code>,</p>
    <li data-md>
     <p><code class="highlight"><c- n>is_constructible_v</c-><c- o>&lt;</c-><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-><c- p>,</c-> <c- n>expected</c-><c- o>&lt;</c-><c- n>U</c-><c- p>,</c-> <c- n>G</c-><c- o>>&amp;&amp;></c-></code> is <code class="highlight">false</code>,</p>
    <li data-md>
     <p><code class="highlight"><c- n>is_constructible_v</c-><c- o>&lt;</c-><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-><c- p>,</c-> <c- k>const</c-> <c- n>expected</c-><c- o>&lt;</c-><c- n>U</c-><c- p>,</c-> <c- n>G</c-><c- o>>&amp;></c-></code> is <code class="highlight">false</code>,</p>
    <li data-md>
     <p><code class="highlight"><c- n>is_constructible_v</c-><c- o>&lt;</c-><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-><c- p>,</c-> <c- k>const</c-> <c- n>expected</c-><c- o>&lt;</c-><c- n>U</c-><c- p>,</c-> <c- n>G</c-><c- o>>&amp;&amp;></c-></code> is <code class="highlight">false</code>,</p>
    <li data-md>
     <p><code class="highlight"><c- n>is_convertible_v</c-><c- o>&lt;</c-><c- n>expected</c-><c- o>&lt;</c-><c- n>U</c-><c- p>,</c-> <c- n>G</c-><c- o>>&amp;</c-><c- p>,</c-> <c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>>></c-></code> is <code class="highlight">false</code>,</p>
    <li data-md>
     <p><code class="highlight"><c- n>is_convertible_v</c-><c- o>&lt;</c-><c- n>expected</c-><c- o>&lt;</c-><c- n>U</c-><c- p>,</c-> <c- n>G</c-><c- o>>&amp;&amp;</c-><c- p>,</c-> <c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>>></c-></code> is <code class="highlight">false</code>,</p>
    <li data-md>
     <p><code class="highlight"><c- n>is_convertible_v</c-><c- o>&lt;</c-><c- k>const</c-> <c- n>expected</c-><c- o>&lt;</c-><c- n>U</c-><c- p>,</c-> <c- n>G</c-><c- o>>&amp;</c-><c- p>,</c-> <c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>>></c-></code> is <code class="highlight">false</code> and</p>
    <li data-md>
     <p><code class="highlight"><c- n>is_convertible_v</c-><c- o>&lt;</c-><c- k>const</c-> <c- n>expected</c-><c- o>&lt;</c-><c- n>U</c-><c- p>,</c-> <c- n>G</c-><c- o>>&amp;&amp;</c-><c- p>,</c-> <c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>>></c-></code> is <code class="highlight">false</code>.</p>
   </ul>
   <p>The constructor is explicit if and only if</p>
   <ul>
    <li data-md>
     <p><code class="highlight"><c- n>T</c-></code> and <code class="highlight"><c- n>U</c-></code> are not <code class="highlight"><c- b>void</c-></code> and <code class="highlight"><c- n>is_convertible_v</c-><c- o>&lt;</c-><c- n>U</c-> <c- k>const</c-><c- o>&amp;</c-><c- p>,</c-> <c- n>T</c-><c- o>></c-></code> is <code class="highlight">false</code> or</p>
    <li data-md>
     <p><code class="highlight"><c- n>is_convertible_v</c-><c- o>&lt;</c-><c- k>const</c-> <c- n>G</c-><c- o>&amp;</c-><c- p>,</c-> <c- n>E</c-><c- o>></c-></code> is <code class="highlight">false</code>.</p>
   </ul>
<pre class="language-c++ highlight"><c- n>template</c-> <c- o>&lt;</c-><c- n>class</c-> <c- n>U</c-><c- p>,</c-> <c- n>class</c-> <c- n>G</c-><c- o>></c->
    <c- n>EXPLICIT</c-> <c- n>constexpr</c-> <c- n>expected</c-><c- p>(</c-><c- n>expected</c-><c- o>&lt;</c-><c- n>U</c-><c- p>,</c-> <c- n>G</c-><c- o>>&amp;&amp;</c-> <c- n>rhs</c-><c- p>);</c->
</pre>
   <p><em>Effects</em>: If <code class="highlight"><c- b>bool</c-><c- p>(</c-><c- n>rhs</c-><c- p>)</c-></code> initializes <code class="highlight"><c- n>val</c-></code> as if
direct-non-list-initializing an object of type <code class="highlight"><c- n>T</c-></code> with the expression <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>move</c-><c- p>(</c-><c- o>*</c-><c- n>rhs</c-><c- p>)</c-></code> or nothing if <code class="highlight"><c- n>T</c-></code> is <code class="highlight"><c- b>void</c-></code>.</p>
   <p>If <code class="highlight"><c- o>!</c-><c- b>bool</c-><c- p>(</c-><c- n>rhs</c-><c- p>)</c-></code>, initializes <code class="highlight"><c- n>unexpect</c-></code> as if
direct-non-list-initializing an object of type <code class="highlight"><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code> with the
expression <code class="highlight"><c- n>unexpected</c-><c- p>(</c-><c- n>std</c-><c- o>::</c-><c- n>move</c-><c- p>(</c-><c- n>rhs</c-><c- p>.</c-><c- n>error</c-><c- p>()))</c-></code>.</p>
   <p><code class="highlight"><c- b>bool</c-><c- p>(</c-><c- n>rhs</c-><c- p>)</c-></code> is unchanged.</p>
   <p><em>Postconditions</em>: <code class="highlight"><c- b>bool</c-><c- p>(</c-><c- n>rhs</c-><c- p>)</c-> <c- o>==</c-> <c- b>bool</c-><c- p>(</c-><c- o>*</c-><c- k>this</c-><c- p>)</c-></code>.</p>
   <p><em>Throws</em>: Any exception thrown by operations specified in the effect clause.</p>
   <p><em>Remarks</em>: This constructor shall not participate in overload resolution unless: <code class="highlight"><c- n>T</c-></code> and <code class="highlight"><c- n>U</c-></code> are <code class="highlight"><c- b>void</c-></code> or</p>
   <ul>
    <li data-md>
     <p><code class="highlight"><c- n>is_constructible_v</c-><c- o>&lt;</c-><c- n>T</c-><c- p>,</c-> <c- n>U</c-><c- o>&amp;&amp;></c-></code> is <code class="highlight">true</code>,</p>
    <li data-md>
     <p><code class="highlight"><c- n>is_constructible_v</c-><c- o>&lt;</c-><c- n>T</c-><c- p>,</c-> <c- n>expected</c-><c- o>&lt;</c-><c- n>U</c-><c- p>,</c-> <c- n>G</c-><c- o>>&amp;></c-></code> is <code class="highlight">false</code>,</p>
    <li data-md>
     <p><code class="highlight"><c- n>is_constructible_v</c-><c- o>&lt;</c-><c- n>T</c-><c- p>,</c-> <c- n>expected</c-><c- o>&lt;</c-><c- n>U</c-><c- p>,</c-> <c- n>G</c-><c- o>>&amp;&amp;></c-></code> is <code class="highlight">false</code>,</p>
    <li data-md>
     <p><code class="highlight"><c- n>is_constructible_v</c-><c- o>&lt;</c-><c- n>T</c-><c- p>,</c-> <c- k>const</c-> <c- n>expected</c-><c- o>&lt;</c-><c- n>U</c-><c- p>,</c-> <c- n>G</c-><c- o>>&amp;></c-></code> is <code class="highlight">false</code>,</p>
    <li data-md>
     <p><code class="highlight"><c- n>is_constructible_v</c-><c- o>&lt;</c-><c- n>T</c-><c- p>,</c-> <c- k>const</c-> <c- n>expected</c-><c- o>&lt;</c-><c- n>U</c-><c- p>,</c-> <c- n>G</c-><c- o>>&amp;&amp;></c-></code> is <code class="highlight">false</code>,</p>
    <li data-md>
     <p><code class="highlight"><c- n>is_convertible_v</c-><c- o>&lt;</c-><c- n>expected</c-><c- o>&lt;</c-><c- n>U</c-><c- p>,</c-> <c- n>G</c-><c- o>>&amp;</c-><c- p>,</c-> <c- n>T</c-><c- o>></c-></code> is <code class="highlight">false</code>,</p>
    <li data-md>
     <p><code class="highlight"><c- n>is_convertible_v</c-><c- o>&lt;</c-><c- n>expected</c-><c- o>&lt;</c-><c- n>U</c-><c- p>,</c-> <c- n>G</c-><c- o>>&amp;&amp;</c-><c- p>,</c-> <c- n>T</c-><c- o>></c-></code> is <code class="highlight">false</code>,</p>
    <li data-md>
     <p><code class="highlight"><c- n>is_convertible_v</c-><c- o>&lt;</c-><c- k>const</c-> <c- n>expected</c-><c- o>&lt;</c-><c- n>U</c-><c- p>,</c-> <c- n>G</c-><c- o>>&amp;</c-><c- p>,</c-> <c- n>T</c-><c- o>></c-></code> is <code class="highlight">false</code>, and</p>
    <li data-md>
     <p><code class="highlight"><c- n>is_convertible_v</c-><c- o>&lt;</c-><c- k>const</c-> <c- n>expected</c-><c- o>&lt;</c-><c- n>U</c-><c- p>,</c-> <c- n>G</c-><c- o>>&amp;&amp;</c-><c- p>,</c-> <c- n>T</c-><c- o>></c-></code> is <code class="highlight">false</code>.</p>
   </ul>
   <p>and</p>
   <ul>
    <li data-md>
     <p><code class="highlight"><c- n>is_constructible_v</c-><c- o>&lt;</c-><c- n>E</c-><c- p>,</c-> <c- n>G</c-><c- o>&amp;&amp;></c-></code> is <code class="highlight">true</code>,</p>
    <li data-md>
     <p><code class="highlight"><c- n>is_constructible_v</c-><c- o>&lt;</c-><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-><c- p>,</c-> <c- n>expected</c-><c- o>&lt;</c-><c- n>U</c-><c- p>,</c-> <c- n>G</c-><c- o>>&amp;></c-></code> is <code class="highlight">false</code>,</p>
    <li data-md>
     <p><code class="highlight"><c- n>is_constructible_v</c-><c- o>&lt;</c-><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-><c- p>,</c-> <c- n>expected</c-><c- o>&lt;</c-><c- n>U</c-><c- p>,</c-> <c- n>G</c-><c- o>>&amp;&amp;></c-></code> is <code class="highlight">false</code>,</p>
    <li data-md>
     <p><code class="highlight"><c- n>is_constructible_v</c-><c- o>&lt;</c-><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-><c- p>,</c-> <c- k>const</c-> <c- n>expected</c-><c- o>&lt;</c-><c- n>U</c-><c- p>,</c-> <c- n>G</c-><c- o>>&amp;></c-></code> is <code class="highlight">false</code>,</p>
    <li data-md>
     <p><code class="highlight"><c- n>is_constructible_v</c-><c- o>&lt;</c-><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-><c- p>,</c-> <c- k>const</c-> <c- n>expected</c-><c- o>&lt;</c-><c- n>U</c-><c- p>,</c-> <c- n>G</c-><c- o>>&amp;&amp;></c-></code> is <code class="highlight">false</code>,</p>
    <li data-md>
     <p><code class="highlight"><c- n>is_convertible_v</c-><c- o>&lt;</c-><c- n>expected</c-><c- o>&lt;</c-><c- n>U</c-><c- p>,</c-> <c- n>G</c-><c- o>>&amp;</c-><c- p>,</c-> <c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>>></c-></code> is <code class="highlight">false</code>,</p>
    <li data-md>
     <p><code class="highlight"><c- n>is_convertible_v</c-><c- o>&lt;</c-><c- n>expected</c-><c- o>&lt;</c-><c- n>U</c-><c- p>,</c-> <c- n>G</c-><c- o>>&amp;&amp;</c-><c- p>,</c-> <c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>>></c-></code> is <code class="highlight">false</code>,</p>
    <li data-md>
     <p><code class="highlight"><c- n>is_convertible_v</c-><c- o>&lt;</c-><c- k>const</c-> <c- n>expected</c-><c- o>&lt;</c-><c- n>U</c-><c- p>,</c-> <c- n>G</c-><c- o>>&amp;</c-><c- p>,</c-> <c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>>></c-></code> is <code class="highlight">false</code> and</p>
    <li data-md>
     <p><code class="highlight"><c- n>is_convertible_v</c-><c- o>&lt;</c-><c- k>const</c-> <c- n>expected</c-><c- o>&lt;</c-><c- n>U</c-><c- p>,</c-> <c- n>G</c-><c- o>>&amp;&amp;</c-><c- p>,</c-> <c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>>></c-></code> is <code class="highlight">false</code>.</p>
   </ul>
   <p>The constructor is explicit if and only if</p>
   <ul>
    <li data-md>
     <p><code class="highlight"><c- n>T</c-></code> and <code class="highlight"><c- n>U</c-></code> are not <code class="highlight"><c- b>void</c-></code> and <code class="highlight"><c- n>is_convertible_v</c-><c- o>&lt;</c-><c- n>U</c-><c- o>&amp;&amp;</c-><c- p>,</c-> <c- n>T</c-><c- o>></c-></code> is <code class="highlight">false</code> or</p>
    <li data-md>
     <p><code class="highlight"><c- n>is_convertible_v</c-><c- o>&lt;</c-><c- n>G</c-><c- o>&amp;&amp;</c-><c- p>,</c-> <c- n>E</c-><c- o>></c-></code> is <code class="highlight">false</code>.</p>
   </ul>
<pre class="language-c++ highlight"><c- n>template</c-> <c- o>&lt;</c-><c- n>class</c-> <c- n>U</c-> <c- o>=</c-> <c- n>T</c-><c- o>></c->
    <c- n>EXPLICIT</c-> <c- n>constexpr</c-> <c- n>expected</c-><c- p>(</c-><c- n>U</c-><c- o>&amp;&amp;</c-> <c- n>v</c-><c- p>);</c->
</pre>
   <p><em>Effects</em>: Initializes <code class="highlight"><c- n>val</c-></code> as if direct-non-list-initializing an
object of type <code class="highlight"><c- n>T</c-></code> with the expression <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>forward</c-><c- o>&lt;</c-><c- n>U</c-><c- o>></c-><c- p>(</c-><c- n>v</c-><c- p>)</c-></code>.</p>
   <p><em>Postconditions</em>: <code class="highlight"><c- b>bool</c-><c- p>(</c-><c- o>*</c-><c- k>this</c-><c- p>)</c-></code> .</p>
   <p><em>Throws</em>: Any exception thrown by the selected constructor of <code class="highlight"><c- n>T</c-></code>.</p>
   <p><em>Remarks</em>: If <code class="highlight"><c- n>T</c-></code>'s selected constructor is a constexpr constructor, this
constructor shall be a constexpr constructor. This constructor shall not
participate in overload resolution unless</p>
   <ul>
    <li data-md>
     <p><code class="highlight"><c- n>T</c-></code> is not <code class="highlight"><c- b>void</c-></code>,</p>
    <li data-md>
     <p><code class="highlight"><c- n>is_constructible_v</c-><c- o>&lt;</c-><c- n>T</c-><c- p>,</c-> <c- n>U</c-><c- o>&amp;&amp;></c-></code> is <code class="highlight">true</code>,</p>
    <li data-md>
     <p><code class="highlight"><c- n>is_same_v</c-><c- o>&lt;</c-><c- n>remove_cvref_t</c-><c- o>&lt;</c-><c- n>U</c-><c- o>></c-><c- p>,</c-> <c- n>in_place_t</c-><c- o>></c-></code> is <code class="highlight">false</code>,</p>
    <li data-md>
     <p><code class="highlight"><c- n>is_same_v</c-><c- o>&lt;</c-><c- n>expected</c-><c- o>&lt;</c-><c- n>T</c-><c- p>,</c-> <c- n>E</c-><c- o>></c-><c- p>,</c-> <c- n>remove_cvref_t</c-><c- o>&lt;</c-><c- n>U</c-><c- o>>></c-></code> is <code class="highlight">false</code> and</p>
    <li data-md>
     <p><code class="highlight"><c- n>is_same_v</c-><c- o>&lt;</c-><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-><c- p>,</c-> <c- n>remove_cvref_t</c-><c- o>&lt;</c-><c- n>U</c-><c- o>>></c-></code> is <code class="highlight">false</code>.</p>
   </ul>
   <p>The constructor is explicit if and only if <code class="highlight"><c- n>is_convertible_v</c-><c- o>&lt;</c-><c- n>U</c-><c- o>&amp;&amp;</c-><c- p>,</c-> <c- n>T</c-><c- o>></c-></code> is <code class="highlight">false</code>.</p>
<pre class="language-c++ highlight"><c- n>template</c-> <c- o>&lt;</c-><c- n>class</c-> <c- n>G</c-> <c- o>=</c-> <c- n>E</c-><c- o>></c->
    <c- n>EXPLICIT</c-> <c- n>constexpr</c-> <c- n>expected</c-><c- p>(</c-><c- k>const</c-> <c- n>unexpected</c-><c- o>&lt;</c-><c- n>G</c-><c- o>>&amp;</c-> <c- n>e</c-><c- p>);</c->
</pre>
   <p><em>Effects</em>: Initializes <code class="highlight"><c- n>unexpect</c-></code> as if direct-non-list-initializing
an object of type <code class="highlight"><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code> with the expression <code class="highlight"><c- n>e</c-></code>.</p>
   <p><em>Postconditions</em>: <code class="highlight"><c- o>!</c-><c- b>bool</c-><c- p>(</c-><c- o>*</c-><c- k>this</c-><c- p>)</c-></code>.</p>
   <p><em>Throws</em>: Any exception thrown by the selected constructor of <code class="highlight"><c- n>E</c-></code>.</p>
   <p><em>Remark</em>: If <code class="highlight"><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code>'s selected constructor is a constexpr constructor,
this constructor shall be a constexpr constructor. This constructor shall not
participate in overload resolution unless <code class="highlight"><c- n>is_constructible_v</c-><c- o>&lt;</c-><c- n>E</c-><c- p>,</c-> <c- k>const</c-> <c- n>G</c-><c- o>&amp;></c-></code> is <code class="highlight">true</code>. The
constructor is explicit if and only if <code class="highlight"><c- n>is_convertible_v</c-><c- o>&lt;</c-><c- k>const</c-> <c- n>G</c-><c- o>&amp;</c-><c- p>,</c-> <c- n>E</c-><c- o>></c-></code> is <code class="highlight">false</code>.</p>
<pre class="language-c++ highlight"><c- n>template</c-> <c- o>&lt;</c-><c- n>class</c-> <c- n>G</c-> <c- o>=</c-> <c- n>E</c-><c- o>></c->
    <c- n>EXPLICIT</c-> <c- n>constexpr</c-> <c- n>expected</c-><c- p>(</c-><c- n>unexpected</c-><c- o>&lt;</c-><c- n>G</c-><c- o>>&amp;&amp;</c-> <c- n>e</c-><c- p>);</c->
</pre>
   <p><em>Effects</em>: Initializes <code class="highlight"><c- n>unexpect</c-></code> as if direct-non-list-initializing
an object of type <code class="highlight"><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code> with the expression <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>move</c-><c- p>(</c-><c- n>e</c-><c- p>)</c-></code>.</p>
   <p><em>Postconditions</em>: <code class="highlight"><c- o>!</c-><c- b>bool</c-><c- p>(</c-><c- o>*</c-><c- k>this</c-><c- p>)</c-></code>.</p>
   <p><em>Throws</em>: Any exception thrown by the selected constructor of <code class="highlight"><c- n>E</c-></code>.</p>
   <p><em>Remark</em>: If <code class="highlight"><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code>'s selected constructor is a constexpr constructor,
this constructor shall be a constexpr constructor. The expression inside <code class="highlight"><c- k>noexcept</c-></code> is equivalent to: <code class="highlight"><c- n>is_nothrow_constructible_v</c-><c- o>&lt;</c-><c- n>E</c-><c- p>,</c-> <c- n>G</c-><c- o>&amp;&amp;></c-></code> is <code class="highlight">true</code>. This
constructor shall not participate in overload resolution unless <code class="highlight"><c- n>is_constructible_v</c-><c- o>&lt;</c-><c- n>E</c-><c- p>,</c-> <c- n>G</c-><c- o>&amp;&amp;></c-></code> is <code class="highlight">true</code>. The constructor is explicit if and only if <code class="highlight"><c- n>is_convertible_v</c-><c- o>&lt;</c-><c- n>G</c-><c- o>&amp;&amp;</c-><c- p>,</c-> <c- n>E</c-><c- o>></c-></code> is <code class="highlight">false</code>.</p>
<pre class="language-c++ highlight"><c- n>template</c-> <c- o>&lt;</c-><c- n>class</c-><c- p>...</c-> <c- n>Args</c-><c- o>></c->
    <c- n>constexpr</c-> <c- n>explicit</c-> <c- n>expected</c-><c- p>(</c-><c- n>in_place_t</c-><c- p>,</c-> <c- n>Args</c-><c- o>&amp;&amp;</c-><c- p>...</c-> <c- n>args</c-><c- p>);</c->
</pre>
   <p><em>Effects</em>: Initializes <code class="highlight"><c- n>val</c-></code> as if direct-non-list-initializing an
object of type <code class="highlight"><c- n>T</c-></code> with the arguments <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>forward</c-><c- o>&lt;</c-><c- n>Args</c-><c- o>></c-><c- p>(</c-><c- n>args</c-><c- p>)...</c-></code> if <code class="highlight"><c- n>T</c-></code> is not <code class="highlight"><c- b>void</c-></code>.</p>
   <p><em>Postconditions</em>: <code class="highlight"><c- b>bool</c-><c- p>(</c-><c- o>*</c-><c- k>this</c-><c- p>)</c-></code> .</p>
   <p><em>Throws</em>: Any exception thrown by the selected constructor of <code class="highlight"><c- n>T</c-></code>.</p>
   <p><em>Remarks</em>: If <code class="highlight"><c- n>T</c-></code>'s constructor selected for the initialization is a constexpr
constructor, this constructor shall be a constexpr constructor. This
constructor shall not participate in overload resolution unless <code class="highlight"><c- n>T</c-></code> is <code class="highlight"><c- b>void</c-></code> and <code class="highlight"><c- k>sizeof</c-><c- p>...(</c-><c- n>Args</c-><c- p>)</c-> <c- o>==</c-> <c- mi>0</c-></code> or <code class="highlight"><c- n>T</c-></code> is not <code class="highlight"><c- b>void</c-></code> and <code class="highlight"><c- n>is_constructible_v</c-><c- o>&lt;</c-><c- n>T</c-><c- p>,</c-> <c- n>Args</c-><c- p>...</c-><c- o>></c-></code> is <code class="highlight">true</code>.</p>
<pre class="language-c++ highlight"><c- n>template</c-> <c- o>&lt;</c-><c- n>class</c-> <c- n>U</c-><c- p>,</c-> <c- n>class</c-><c- p>...</c-> <c- n>Args</c-><c- o>></c->
    <c- n>constexpr</c-> <c- n>explicit</c-> <c- n>expected</c-><c- p>(</c-><c- n>in_place_t</c-><c- p>,</c-> <c- n>initializer_list</c-><c- o>&lt;</c-><c- n>U</c-><c- o>></c-> <c- n>il</c-><c- p>,</c-> <c- n>Args</c-><c- o>&amp;&amp;</c-><c- p>...</c-> <c- n>args</c-><c- p>);</c->
</pre>
   <p><em>Effects</em>: Initializes <code class="highlight"><c- n>val</c-></code> as if direct-non-list-initializing an
object of type <code class="highlight"><c- n>T</c-></code> with the arguments <code class="highlight"><c- n>il</c-><c- p>,</c-> <c- n>std</c-><c- o>::</c-><c- n>forward</c-><c- o>&lt;</c-><c- n>Args</c-><c- o>></c-><c- p>(</c-><c- n>args</c-><c- p>)...</c-></code>.</p>
   <p><em>Postconditions</em>: <code class="highlight"><c- b>bool</c-><c- p>(</c-><c- o>*</c-><c- k>this</c-><c- p>)</c-></code> .</p>
   <p><em>Throws</em>: Any exception thrown by the selected constructor of <code class="highlight"><c- n>T</c-></code>.</p>
   <p><em>Remarks</em>: If <code class="highlight"><c- n>T</c-></code>'s constructor selected for the initialization is a constexpr
constructor, this constructor shall be a constexpr constructor. This
constructor shall not participate in overload resolution unless <code class="highlight"><c- n>T</c-></code> is not <code class="highlight"><c- b>void</c-></code> and <code class="highlight"><c- n>is_constructible_v</c-><c- o>&lt;</c-><c- n>T</c-><c- p>,</c-> <c- n>initializer_list</c-><c- o>&lt;</c-><c- n>U</c-><c- o>>&amp;</c-><c- p>,</c-> <c- n>Args</c-><c- p>...</c-><c- o>></c-></code> is <code class="highlight">true</code>.</p>
<pre class="language-c++ highlight"><c- n>template</c-> <c- o>&lt;</c-><c- n>class</c-><c- p>...</c-> <c- n>Args</c-><c- o>></c->
    <c- n>constexpr</c-> <c- n>explicit</c-> <c- n>expected</c-><c- p>(</c-><c- n>unexpect_t</c-><c- p>,</c-> <c- n>Args</c-><c- o>&amp;&amp;</c-><c- p>...</c-> <c- n>args</c-><c- p>);</c->
</pre>
   <p><em>Effects</em>: Initializes <code class="highlight"><c- n>unexpect</c-></code> as if direct-non-list-initializing
an object of type <code class="highlight"><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code>with the arguments <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>forward</c-><c- o>&lt;</c-><c- n>Args</c-><c- o>></c-><c- p>(</c-><c- n>args</c-><c- p>)...</c-></code>.</p>
   <p><em>Postconditions</em>: <code class="highlight"><c- o>!</c-><c- b>bool</c-><c- p>(</c-><c- o>*</c-><c- k>this</c-><c- p>)</c-></code>.</p>
   <p><em>Throws</em>: Any exception thrown by the selected constructor of <code class="highlight"><c- n>E</c-></code>.</p>
   <p><em>Remarks</em>: If <code class="highlight"><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code>'s constructor selected for the initialization is a
constexpr constructor, this constructor shall be a constexpr constructor. This
constructor shall not participate in overload resolution unless <code class="highlight"><c- n>is_constructible_v</c-><c- o>&lt;</c-><c- n>E</c-><c- p>,</c-> <c- n>Args</c-><c- o>&amp;&amp;</c-><c- p>...</c-><c- o>></c-></code> is <code class="highlight">true</code>.</p>
<pre class="language-c++ highlight"><c- n>template</c-> <c- o>&lt;</c-><c- n>class</c-> <c- n>U</c-><c- p>,</c-> <c- n>class</c-><c- p>...</c-> <c- n>Args</c-><c- o>></c->
    <c- n>constexpr</c-> <c- n>explicit</c-> <c- n>expected</c-><c- p>(</c-><c- n>unexpect_t</c-><c- p>,</c-> <c- n>initializer_list</c-><c- o>&lt;</c-><c- n>U</c-><c- o>></c-> <c- n>il</c-><c- p>,</c-> <c- n>Args</c-><c- o>&amp;&amp;</c-><c- p>...</c-> <c- n>args</c-><c- p>);</c->
</pre>
   <p><em>Effects</em>: Initializes <code class="highlight"><c- n>unexpect</c-></code> as if direct-non-list-initializing
an object of type <code class="highlight"><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code> with the arguments <code class="highlight"><c- n>il</c-><c- p>,</c-> <c- n>std</c-><c- o>::</c-><c- n>forward</c-><c- o>&lt;</c-><c- n>Args</c-><c- o>></c-><c- p>(</c-><c- n>args</c-><c- p>)...</c-></code>.</p>
   <p><em>Postconditions</em>: <code class="highlight"><c- o>!</c-><c- b>bool</c-><c- p>(</c-><c- o>*</c-><c- k>this</c-><c- p>)</c-></code>.</p>
   <p><em>Throws</em>: Any exception thrown by the selected constructor of <code class="highlight"><c- n>E</c-></code>.</p>
   <p><em>Remarks</em>: If <code class="highlight"><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code>'s constructor selected for the initialization is a
constexpr constructor, this constructor shall be a constexpr constructor. This
constructor shall not participate in overload resolution unless <code class="highlight"><c- n>is_constructible_v</c-><c- o>&lt;</c-><c- n>E</c-><c- p>,</c-> <c- n>initializer_list</c-><c- o>&lt;</c-><c- n>U</c-><c- o>>&amp;</c-><c- p>,</c-> <c- n>Args</c-><c- o>&amp;&amp;</c-><c- p>...</c-><c- o>></c-></code> is <code class="highlight">true</code>.</p>
   <h3 class="heading settled" data-level="1.7" id="expected.object.dtor"><span class="secno">1.7. </span><span class="content">�.�.4.2 Destructor [<em>expected.object.dtor</em>]</span><a class="self-link" href="#expected.object.dtor"></a></h3>
<pre class="language-c++ highlight"><c- o>~</c-><c- n>expected</c-><c- p>();</c->
</pre>
   <p><em>Effects</em>: If <code class="highlight"><c- n>T</c-></code> is not <code class="highlight"><c- b>void</c-></code> and <code class="highlight"><c- n>is_trivially_destructible_v</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-></code> is <code class="highlight">false</code> and <code class="highlight"><c- b>bool</c-><c- p>(</c-><c- o>*</c-><c- k>this</c-><c- p>)</c-></code>, calls <code class="highlight"><c- n>val</c-><c- p>.</c-><c- o>~</c-><c- n>T</c-><c- p>()</c-></code>. If <code class="highlight"><c- n>is_trivially_destructible_v</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code> is <code class="highlight">false</code> and <code class="highlight"><c- o>!</c-><c- b>bool</c-><c- p>(</c-><c- o>*</c-><c- k>this</c-><c- p>)</c-></code>, calls <code class="highlight"><c- n>unexpect</c-><c- p>.</c-><c- o>~</c-><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-><c- p>()</c-></code>.</p>
   <p><em>Remarks</em>: If <code class="highlight"><c- n>T</c-></code> is <code class="highlight"><c- b>void</c-></code> or <code class="highlight"><c- n>is_trivially_destructible_v</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-></code> is <code class="highlight">true</code> and <code class="highlight"><c- n>is_trivially_destructible_v</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code> is <code class="highlight">true</code> then this destructor shall be a
trivial destructor.</p>
   <h3 class="heading settled" data-level="1.8" id="expected.object.assign"><span class="secno">1.8. </span><span class="content">�.�.4.3 Assignment [<em>expected.object.assign</em>]</span><a class="self-link" href="#expected.object.assign"></a></h3>
<pre class="language-c++ highlight"><c- n>expected</c-><c- o>&amp;</c-> <c- n>operator</c-><c- o>=</c-><c- p>(</c-><c- k>const</c-> <c- n>expected</c-><c- o>&amp;</c-> <c- n>rhs</c-><c- p>)</c-> <c- n>noexcept</c-><c- p>(</c-><c- n>see</c-> <c- n>below</c-><c- p>);</c->
</pre>
   <p><em>Effects</em>:</p>
   <p>If <code class="highlight"><c- b>bool</c-><c- p>(</c-><c- o>*</c-><c- k>this</c-><c- p>)</c-></code> and <code class="highlight"><c- b>bool</c-><c- p>(</c-><c- n>rhs</c-><c- p>)</c-></code>,</p>
   <ul>
    <li data-md>
     <p>assigns <code class="highlight"><c- o>*</c-><c- n>rhs</c-></code> to <code class="highlight"><c- n>val</c-></code> if <code class="highlight"><c- n>T</c-></code> is not <code class="highlight"><c- b>void</c-></code>;</p>
   </ul>
   <p>otherwise if <code class="highlight"><c- o>!</c-><c- b>bool</c-><c- p>(</c-><c- o>*</c-><c- k>this</c-><c- p>)</c-></code> and <code class="highlight"><c- o>!</c-><c- b>bool</c-><c- p>(</c-><c- n>rhs</c-><c- p>)</c-></code>,</p>
   <ul>
    <li data-md>
     <p>assigns <code class="highlight"><c- n>unexpected</c-><c- p>(</c-><c- n>rhs</c-><c- p>.</c-><c- n>error</c-><c- p>())</c-></code> to <code class="highlight"><c- n>unexpect</c-></code>;</p>
   </ul>
   <p>otherwise if <code class="highlight"><c- b>bool</c-><c- p>(</c-><c- o>*</c-><c- k>this</c-><c- p>)</c-></code> and <code class="highlight"><c- o>!</c-><c- b>bool</c-><c- p>(</c-><c- n>rhs</c-><c- p>)</c-></code>,</p>
   <ul>
    <li data-md>
     <p>if <code class="highlight"><c- n>T</c-></code> is <code class="highlight"><c- b>void</c-></code></p>
     <ul>
      <li data-md>
       <p>initializes <code class="highlight"><c- n>unexpect</c-></code> as if direct-non-list-initializing an object of type <code class="highlight"><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code> with <code class="highlight"><c- n>unexpected</c-><c- p>(</c-><c- n>rhs</c-><c- p>.</c-><c- n>error</c-><c- p>())</c-></code>. Either</p>
      <li data-md>
       <p>the constructor didn’t throw, set <code class="highlight"><c- n>has_val</c-></code> to <code class="highlight">false</code>, or</p>
      <li data-md>
       <p>the constructor did throw, and nothing was changed.</p>
     </ul>
    <li data-md>
     <p>otherwise if <code class="highlight"><c- n>is_nothrow_copy_constructible_v</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code> is <code class="highlight">true</code></p>
     <ul>
      <li data-md>
       <p>destroys <code class="highlight"><c- n>val</c-></code> by calling <code class="highlight"><c- n>val</c-><c- p>.</c-><c- o>~</c-><c- n>T</c-><c- p>()</c-></code>,</p>
      <li data-md>
       <p>initializes <code class="highlight"><c- n>unexpect</c-></code> as if direct-non-list-initializing an object of type <code class="highlight"><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code> with <code class="highlight"><c- n>unexpected</c-><c- p>(</c-><c- n>rhs</c-><c- p>.</c-><c- n>error</c-><c- p>())</c-></code> and set <code class="highlight"><c- n>has_val</c-></code> to <code class="highlight">false</code>.</p>
     </ul>
    <li data-md>
     <p>otherwise if <code class="highlight"><c- n>is_nothrow_move_constructible_v</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code> is <code class="highlight">true</code></p>
     <ul>
      <li data-md>
       <p>constructs a <code class="highlight"><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-> <c- n>tmp</c-></code> from <code class="highlight"><c- n>unexpected</c-><c- p>(</c-><c- n>rhs</c-><c- p>.</c-><c- n>error</c-><c- p>())</c-></code> (this can throw),</p>
      <li data-md>
       <p>destroys <code class="highlight"><c- n>val</c-></code> by calling <code class="highlight"><c- n>val</c-><c- p>.</c-><c- o>~</c-><c- n>T</c-><c- p>()</c-></code>,</p>
      <li data-md>
       <p>initializes <code class="highlight"><c- n>unexpect</c-></code> as if direct-non-list-initializing an object of type <code class="highlight"><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code> with <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>move</c-><c- p>(</c-><c- n>tmp</c-><c- p>)</c-></code> and set <code class="highlight"><c- n>has_val</c-></code> to <code class="highlight">false</code>.</p>
     </ul>
   </ul>
   <p>otherwise</p>
   <ul>
    <li data-md>
     <p>constructs a <code class="highlight"><c- n>T</c-> <c- n>tmp</c-></code> from <code class="highlight"><c- o>*</c-><c- k>this</c-></code> (this can throw),</p>
    <li data-md>
     <p>destroys <code class="highlight"><c- n>val</c-></code> by calling <code class="highlight"><c- n>val</c-><c- p>.</c-><c- o>~</c-><c- n>T</c-><c- p>()</c-></code>,</p>
    <li data-md>
     <p>initializes <code class="highlight"><c- n>unexpect</c-></code> as if direct-non-list-initializing an object of type <code class="highlight"><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code> with <code class="highlight"><c- n>unexpected</c-><c- p>(</c-><c- n>rhs</c-><c- p>.</c-><c- n>error</c-><c- p>())</c-></code>. Either,</p>
     <ul>
      <li data-md>
       <p>the last constructor didn’t throw, set <code class="highlight"><c- n>has_val</c-></code> to <code class="highlight">false</code>, or</p>
      <li data-md>
       <p>the last constructor did throw, so move-construct the <code class="highlight"><c- n>T</c-></code> from <code class="highlight"><c- n>tmp</c-></code> back into the expected storage (which can’t throw as <code class="highlight"><c- n>is_nothrow_move_constructible_v</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-></code> is <code class="highlight">true</code>), and rethrow the exception.</p>
     </ul>
   </ul>
   <p>otherwise</p>
   <ul>
    <li data-md>
     <p>if <code class="highlight"><c- n>T</c-></code> is <code class="highlight"><c- b>void</c-></code> destroys <code class="highlight"><c- n>unexpect</c-></code> by calling <code class="highlight"><c- n>unexpect</c-><c- p>.</c-><c- o>~</c-><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-><c- p>()</c-></code> and set <code class="highlight"><c- n>has_val</c-></code> to <code class="highlight">true</code>,</p>
    <li data-md>
     <p>otherwise if <code class="highlight"><c- n>is_nothrow_copy_constructible_v</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-></code> is <code class="highlight">true</code></p>
     <ul>
      <li data-md>
       <p>destroys <code class="highlight"><c- n>unexpect</c-></code> by calling <code class="highlight"><c- n>unexpect</c-><c- p>.</c-><c- o>~</c-><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-><c- p>()</c-></code></p>
      <li data-md>
       <p>initializes <code class="highlight"><c- n>val</c-></code> as if direct-non-list-initializing an object of type <code class="highlight"><c- n>T</c-></code> with <code class="highlight"><c- o>*</c-><c- n>rhs</c-></code>;</p>
     </ul>
    <li data-md>
     <p>otherwise if <code class="highlight"><c- n>is_nothrow_move_constructible_v</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-></code> is <code class="highlight">true</code></p>
     <ul>
      <li data-md>
       <p>constructs a <code class="highlight"><c- n>T</c-> <c- n>tmp</c-></code> from <code class="highlight"><c- o>*</c-><c- n>rhs</c-></code> (this can throw),</p>
      <li data-md>
       <p>destroys <code class="highlight"><c- n>unexpect</c-></code> by calling <code class="highlight"><c- n>unexpect</c-><c- p>.</c-><c- o>~</c-><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-><c- p>()</c-></code></p>
      <li data-md>
       <p>initializes <code class="highlight"><c- n>val</c-></code> as if direct-non-list-initializing an object of type <code class="highlight"><c- n>T</c-></code> with <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>move</c-><c- p>(</c-><c- n>tmp</c-><c- p>)</c-></code>;</p>
     </ul>
    <li data-md>
     <p>otherwise</p>
     <ul>
      <li data-md>
       <p>constructs a <code class="highlight"><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-> <c- n>tmp</c-></code> from <code class="highlight"><c- n>unexpected</c-><c- p>(</c-><c- k>this</c-><c- o>-></c-><c- n>error</c-><c- p>())</c-></code> (which can throw),</p>
      <li data-md>
       <p>destroys <code class="highlight"><c- n>unexpect</c-></code> by calling <code class="highlight"><c- n>unexpect</c-><c- p>.</c-><c- o>~</c-><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-><c- p>()</c-></code>,</p>
      <li data-md>
       <p>initializes <code class="highlight"><c- n>val</c-></code> as if direct-non-list-initializing an object of type <code class="highlight"><c- n>T</c-></code> with <code class="highlight"><c- o>*</c-><c- n>rhs</c-></code>. Either,</p>
      <li data-md>
       <p>the constructor didn’t throw, set <code class="highlight"><c- n>has_val</c-></code> to <code class="highlight">true</code>, or</p>
      <li data-md>
       <p>the constructor did throw, so move-construct the <code class="highlight"><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code> from <code class="highlight"><c- n>tmp</c-></code> back into the expected storage (which can’t throw as <code class="highlight"><c- n>is_nothrow_move_constructible_v</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code> is <code class="highlight">true</code>), and rethrow the exception.</p>
     </ul>
   </ul>
   <p><em>Returns</em>: <code class="highlight"><c- o>*</c-><c- k>this</c-></code>.</p>
   <p><em>Postconditions</em>: <code class="highlight"><c- b>bool</c-><c- p>(</c-><c- n>rhs</c-><c- p>)</c-> <c- o>==</c-> <c- b>bool</c-><c- p>(</c-><c- o>*</c-><c- k>this</c-><c- p>)</c-></code>.</p>
   <p><em>Throws</em>: Any exception thrown by the operations specified in the effect clause.</p>
   <p><em>Remarks</em>: If any exception is thrown, <code class="highlight"><c- b>bool</c-><c- p>(</c-><c- o>*</c-><c- k>this</c-><c- p>)</c-></code> and <code class="highlight"><c- b>bool</c-><c- p>(</c-><c- n>rhs</c-><c- p>)</c-></code> remain unchanged.</p>
   <p>If an exception is thrown during the call to <code class="highlight"><c- n>T</c-></code>'s or <code class="highlight"><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code>'s copy
constructor, no effect. If an exception is thrown during the call to <code class="highlight"><c- n>T</c-></code>'s or <code class="highlight"><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code>'s copy assignment, the state of its contained value is as defined
by the exception safety guarantee of <code class="highlight"><c- n>T</c-></code>'s or <code class="highlight"><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code>'s copy assignment.</p>
   <p>This operator shall be defined as deleted unless</p>
   <ul>
    <li data-md>
     <p><code class="highlight"><c- n>T</c-></code> is <code class="highlight"><c- b>void</c-></code> and <code class="highlight"><c- n>is_copy_assignable_v</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code> is <code class="highlight">true</code> and <code class="highlight"><c- n>is_copy_constructible_v</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code> is <code class="highlight">true</code> or</p>
    <li data-md>
     <p><code class="highlight"><c- n>T</c-></code> is not <code class="highlight"><c- b>void</c-></code> and <code class="highlight"><c- n>is_copy_assignable_v</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-></code> is <code class="highlight">true</code> and <code class="highlight"><c- n>is_copy_constructible_v</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-></code> is <code class="highlight">true</code> and <code class="highlight"><c- n>is_copy_assignable_v</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code> is <code class="highlight">true</code> and <code class="highlight"><c- n>is_copy_constructible_v</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code> is <code class="highlight">true</code> and
(<code class="highlight"><c- n>is_nothrow_move_constructible_v</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code> is <code class="highlight">true</code> or <code class="highlight"><c- n>is_nothrow_move_constructible_v</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-></code> is <code class="highlight">true</code>).</p>
   </ul>
<pre class="language-c++ highlight"><c- n>expected</c-><c- o>&amp;</c-> <c- n>operator</c-><c- o>=</c-><c- p>(</c-><c- n>expected</c-><c- o>&amp;&amp;</c-> <c- n>rhs</c-><c- p>)</c-> <c- n>noexcept</c-><c- p>(</c-><c- n>see</c-> <c- n>below</c-><c- p>);</c->
</pre>
   <p><em>Effects</em>:</p>
   <p>If <code class="highlight"><c- b>bool</c-><c- p>(</c-><c- o>*</c-><c- k>this</c-><c- p>)</c-></code> and <code class="highlight"><c- b>bool</c-><c- p>(</c-><c- n>rhs</c-><c- p>)</c-></code>,</p>
   <ul>
    <li data-md>
     <p>move assign <code class="highlight"><c- o>*</c-><c- n>rhs</c-></code> to <code class="highlight"><c- n>val</c-></code> if <code class="highlight"><c- n>T</c-></code> is not <code class="highlight"><c- b>void</c-></code>;</p>
   </ul>
   <p>otherwise if <code class="highlight"><c- o>!</c-><c- b>bool</c-><c- p>(</c-><c- o>*</c-><c- k>this</c-><c- p>)</c-></code> and <code class="highlight"><c- o>!</c-><c- b>bool</c-><c- p>(</c-><c- n>rhs</c-><c- p>)</c-></code>,</p>
   <ul>
    <li data-md>
     <p>move assign <code class="highlight"><c- n>unexpected</c-><c- p>(</c-><c- n>rhs</c-><c- p>.</c-><c- n>error</c-><c- p>())</c-></code> to <code class="highlight"><c- n>unexpect</c-></code>;</p>
   </ul>
   <p>otherwise if <code class="highlight"><c- b>bool</c-><c- p>(</c-><c- o>*</c-><c- k>this</c-><c- p>)</c-></code> and <code class="highlight"><c- o>!</c-><c- b>bool</c-><c- p>(</c-><c- n>rhs</c-><c- p>)</c-></code>,</p>
   <ul>
    <li data-md>
     <p>if <code class="highlight"><c- n>T</c-></code> is <code class="highlight"><c- b>void</c-></code></p>
     <ul>
      <li data-md>
       <p>initializes <code class="highlight"><c- n>unexpect</c-></code> as if direct-non-list-initializing an object of type <code class="highlight"><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code> with <code class="highlight"><c- n>unexpected</c-><c- p>(</c-><c- n>move</c-><c- p>(</c-><c- n>rhs</c-><c- p>).</c-><c- n>error</c-><c- p>())</c-></code>. Either</p>
      <li data-md>
       <p>the constructor didn’t throw, set <code class="highlight"><c- n>has_val</c-></code> to <code class="highlight">false</code>, or</p>
      <li data-md>
       <p>the constructor did throw, and nothing was changed.</p>
     </ul>
    <li data-md>
     <p>otherwise if <code class="highlight"><c- n>is_nothrow_move_constructible_v</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code> is <code class="highlight">true</code></p>
     <ul>
      <li data-md>
       <p>destroys <code class="highlight"><c- n>val</c-></code> by calling <code class="highlight"><c- n>val</c-><c- p>.</c-><c- o>~</c-><c- n>T</c-><c- p>()</c-></code>,</p>
      <li data-md>
       <p>initializes <code class="highlight"><c- n>unexpect</c-></code> as if direct-non-list-initializing an object of type <code class="highlight"><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code> with <code class="highlight"><c- n>unexpected</c-><c- p>(</c-><c- n>std</c-><c- o>::</c-><c- n>move</c-><c- p>(</c-><c- n>rhs</c-><c- p>.</c-><c- n>error</c-><c- p>()))</c-></code>;</p>
     </ul>
    <li data-md>
     <p>otherwise</p>
     <ul>
      <li data-md>
       <p>move constructs a <code class="highlight"><c- n>T</c-> <c- n>tmp</c-></code> from <code class="highlight"><c- o>*</c-><c- k>this</c-></code> (which can’t throw as <code class="highlight"><c- n>T</c-></code> is nothrow-move-constructible),</p>
      <li data-md>
       <p>destroys <code class="highlight"><c- n>val</c-></code> by calling <code class="highlight"><c- n>val</c-><c- p>.</c-><c- o>~</c-><c- n>T</c-><c- p>()</c-></code>,</p>
      <li data-md>
       <p>initializes <code class="highlight"><c- n>unexpect</c-></code> as if direct-non-list-initializing an object of type <code class="highlight"><c- n>unexpected_type</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code> with <code class="highlight"><c- n>unexpected</c-><c- p>(</c-><c- n>std</c-><c- o>::</c-><c- n>move</c-><c- p>(</c-><c- n>rhs</c-><c- p>.</c-><c- n>error</c-><c- p>()))</c-></code>. Either,</p>
      <li data-md>
       <p>The constructor didn’t throw, so mark the expected as holding a <code class="highlight"><c- n>unexpected_type</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code>, or</p>
      <li data-md>
       <p>The constructor did throw, so move-construct the <code class="highlight"><c- n>T</c-></code> from <code class="highlight"><c- n>tmp</c-></code> back into the expected storage (which can’t throw as <code class="highlight"><c- n>T</c-></code> is nothrow-move-constructible), and rethrow the exception.</p>
     </ul>
   </ul>
   <p>otherwise <code class="highlight"><c- o>!</c-><c- b>bool</c-><c- p>(</c-><c- o>*</c-><c- k>this</c-><c- p>)</c-></code> and <code class="highlight"><c- b>bool</c-><c- p>(</c-><c- n>rhs</c-><c- p>)</c-></code>,</p>
   <ul>
    <li data-md>
     <p>if <code class="highlight"><c- n>T</c-></code> is <code class="highlight"><c- b>void</c-></code> destroys <code class="highlight"><c- n>unexpect</c-></code> by calling <code class="highlight"><c- n>unexpect</c-><c- p>.</c-><c- o>~</c-><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-><c- p>()</c-></code></p>
    <li data-md>
     <p>otherwise if <code class="highlight"><c- n>is_nothrow_move_constructible_v</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-></code> is <code class="highlight">true</code></p>
     <ul>
      <li data-md>
       <p>destroys <code class="highlight"><c- n>unexpect</c-></code> by calling <code class="highlight"><c- n>unexpect</c-><c- p>.</c-><c- o>~</c-><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-><c- p>()</c-></code>,</p>
      <li data-md>
       <p>initializes <code class="highlight"><c- n>val</c-></code> as if direct-non-list-initializing an object of type <code class="highlight"><c- n>T</c-></code> with <code class="highlight"><c- o>*</c-><c- n>std</c-><c- o>::</c-><c- n>move</c-><c- p>(</c-><c- n>rhs</c-><c- p>)</c-></code>;</p>
     </ul>
    <li data-md>
     <p>otherwise</p>
     <ul>
      <li data-md>
       <p>move constructs a <code class="highlight"><c- n>unpepected_type</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-> <c- n>tmp</c-></code> from <code class="highlight"><c- n>unexpected</c-><c- p>(</c-><c- k>this</c-><c- o>-></c-><c- n>error</c-><c- p>())</c-></code> (which can’t throw as <code class="highlight"><c- n>E</c-></code> is nothrow-move-constructible),</p>
      <li data-md>
       <p>destroys <code class="highlight"><c- n>unexpect</c-></code> by calling <code class="highlight"><c- n>unexpect</c-><c- p>.</c-><c- o>~</c-><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-><c- p>()</c-></code>,</p>
      <li data-md>
       <p>initializes <code class="highlight"><c- n>val</c-></code> as if direct-non-list-initializing an object of type <code class="highlight"><c- n>T</c-></code> with <code class="highlight"><c- o>*</c-><c- n>std</c-><c- o>::</c-><c- n>move</c-><c- p>(</c-><c- n>rhs</c-><c- p>)</c-></code>. Either,</p>
      <li data-md>
       <p>The constructor didn’t throw, set <code class="highlight"><c- n>has_val</c-></code> to <code class="highlight">true</code>, or</p>
      <li data-md>
       <p>The constructor did throw, so move-construct the <code class="highlight"><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code> from <code class="highlight"><c- n>tmp</c-></code> back into the expected storage (which can’t throw as <code class="highlight"><c- n>E</c-></code> is nothrow-move-constructible), and rethrow the exception.</p>
     </ul>
   </ul>
   <p><em>Returns</em>: <code class="highlight"><c- o>*</c-><c- k>this</c-></code>.</p>
   <p><em>Postconditions</em>: <code class="highlight"><c- b>bool</c-><c- p>(</c-><c- n>rhs</c-><c- p>)</c-> <c- o>==</c-> <c- b>bool</c-><c- p>(</c-><c- o>*</c-><c- k>this</c-><c- p>)</c-></code>.</p>
   <p><em>Remarks</em>: The expression inside noexcept is equivalent to: <code class="highlight"><c- n>is_nothrow_move_assignable_v</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-></code> is <code class="highlight">true</code> and <code class="highlight"><c- n>is_nothrow_move_constructible_v</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-></code> is <code class="highlight">true</code>.</p>
   <p>If any exception is thrown, <code class="highlight"><c- b>bool</c-><c- p>(</c-><c- o>*</c-><c- k>this</c-><c- p>)</c-></code> and <code class="highlight"><c- b>bool</c-><c- p>(</c-><c- n>rhs</c-><c- p>)</c-></code> remain
unchanged. If an exception is thrown during the call to <code class="highlight"><c- n>T</c-></code>'s copy constructor,
no effect. If an exception is thrown during the call to <code class="highlight"><c- n>T</c-></code>'s copy assignment,
the state of its contained value is as defined by the exception safety guarantee
of <code class="highlight"><c- n>T</c-></code>'s copy assignment. If an exception is thrown during the call to <code class="highlight"><c- n>E</c-></code>'s
copy assignment, the state of its contained <code class="highlight"><c- n>unexpect</c-></code> is as defined by
the exception safety guarantee of <code class="highlight"><c- n>E</c-></code>'s copy assignment.</p>
   <p>This operator shall be defined as deleted unless</p>
   <ul>
    <li data-md>
     <p><code class="highlight"><c- n>T</c-></code> is <code class="highlight"><c- b>void</c-></code> and <code class="highlight"><c- n>is_nothrow_move_constructible_v</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code> is <code class="highlight">true</code> and <code class="highlight"><c- n>is_nothrow_move_assignable_v</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code> is <code class="highlight">true</code>.</p>
   </ul>
   <p>or</p>
   <ul>
    <li data-md>
     <p><code class="highlight"><c- n>T</c-></code> is not <code class="highlight"><c- b>void</c-></code> and <code class="highlight"><c- n>is_move_constructible_v</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-></code> is <code class="highlight">true</code> and <code class="highlight"><c- n>is_move_assignable_v</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-></code> is <code class="highlight">true</code> and <code class="highlight"><c- n>is_nothrow_move_constructible_v</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code> is <code class="highlight">true</code> and <code class="highlight"><c- n>is_nothrow_move_assignable_v</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code> is <code class="highlight">true</code>.</p>
   </ul>
<pre class="language-c++ highlight"><c- n>template</c-> <c- o>&lt;</c-><c- n>class</c-> <c- n>U</c-> <c- o>=</c-> <c- n>T</c-><c- o>></c->
    <c- n>expected</c-><c- o>&lt;</c-><c- n>T</c-><c- p>,</c-> <c- n>E</c-><c- o>>&amp;</c-> <c- n>operator</c-><c- o>=</c-><c- p>(</c-><c- n>U</c-><c- o>&amp;&amp;</c-> <c- n>v</c-><c- p>);</c->
</pre>
   <p><em>Effects</em>:</p>
   <p>If <code class="highlight"><c- b>bool</c-><c- p>(</c-><c- o>*</c-><c- k>this</c-><c- p>)</c-></code>, assigns <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>forward</c-><c- o>&lt;</c-><c- n>U</c-><c- o>></c-><c- p>(</c-><c- n>v</c-><c- p>)</c-></code> to <code class="highlight"><c- n>val</c-></code>;</p>
   <p>otherwise if <code class="highlight"><c- n>is_nothrow_constructible_v</c-><c- o>&lt;</c-><c- n>T</c-><c- p>,</c-> <c- n>U</c-><c- o>&amp;&amp;></c-></code> is <code class="highlight">true</code></p>
   <ul>
    <li data-md>
     <p>destroys <code class="highlight"><c- n>unexpect</c-></code> by calling <code class="highlight"><c- n>unexpect</c-><c- p>.</c-><c- o>~</c-><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-><c- p>()</c-></code>,</p>
    <li data-md>
     <p>initializes <code class="highlight"><c- n>val</c-></code> as if direct-non-list-initializing an object of type <code class="highlight"><c- n>T</c-></code> with <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>forward</c-><c- o>&lt;</c-><c- n>U</c-><c- o>></c-><c- p>(</c-><c- n>v</c-><c- p>)</c-></code> and</p>
    <li data-md>
     <p>set <code class="highlight"><c- n>has_val</c-></code> to <code class="highlight">true</code>;</p>
   </ul>
   <p>otherwise</p>
   <ul>
    <li data-md>
     <p>move constructs a <code class="highlight"><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-> <c- n>tmp</c-></code> from <code class="highlight"><c- n>unexpected</c-><c- p>(</c-><c- k>this</c-><c- o>-></c-><c- n>error</c-><c- p>())</c-></code> (which can’t throw as <code class="highlight"><c- n>E</c-></code> is nothrow-move-constructible),</p>
    <li data-md>
     <p>destroys <code class="highlight"><c- n>unexpect</c-></code> by calling <code class="highlight"><c- n>unexpect</c-><c- p>.</c-><c- o>~</c-><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-><c- p>()</c-></code>,</p>
    <li data-md>
     <p>initializes <code class="highlight"><c- n>val</c-></code> as if direct-non-list-initializing an object of type <code class="highlight"><c- n>T</c-></code> with <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>forward</c-><c- o>&lt;</c-><c- n>U</c-><c- o>></c-><c- p>(</c-><c- n>v</c-><c- p>)</c-></code>. Either,</p>
     <ul>
      <li data-md>
       <p>the constructor didn’t throw, set <code class="highlight"><c- n>has_val</c-></code> to <code class="highlight">true</code>, that is set <code class="highlight"><c- n>has_val</c-></code> to <code class="highlight">true</code>, or</p>
      <li data-md>
       <p>the constructor did throw, so move construct the <code class="highlight"><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code> from <code class="highlight"><c- n>tmp</c-></code> back into the expected storage (which can’t throw as <code class="highlight"><c- n>E</c-></code> is nothrow-move-constructible), and re-throw the exception.</p>
     </ul>
   </ul>
   <p><em>Returns</em>: <code class="highlight"><c- o>*</c-><c- k>this</c-></code>.</p>
   <p><em>Postconditions</em>: <code class="highlight"><c- b>bool</c-><c- p>(</c-><c- o>*</c-><c- k>this</c-><c- p>)</c-></code> .</p>
   <p><em>Remarks</em>: If any exception is thrown, <code class="highlight"><c- b>bool</c-><c- p>(</c-><c- o>*</c-><c- k>this</c-><c- p>)</c-></code> remains
 unchanged. If an exception is thrown during the call to <code class="highlight"><c- n>T</c-></code>'s constructor, no
 effect. If an exception is thrown during the call to <code class="highlight"><c- n>T</c-></code>'s copy assignment, the
 state of its contained value is as defined by the exception safety guarantee of <code class="highlight"><c- n>T</c-></code>'s copy assignment.</p>
   <p>This function shall not participate in overload resolution unless:</p>
   <ul>
    <li data-md>
     <p><code class="highlight"><c- n>is_void_v</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-></code> is <code class="highlight">false</code> and</p>
    <li data-md>
     <p><code class="highlight"><c- n>is_same_v</c-><c- o>&lt;</c-><c- n>expected</c-><c- o>&lt;</c-><c- n>T</c-><c- p>,</c-><c- n>E</c-><c- o>></c-><c- p>,</c-> <c- n>remove_cvref_t</c-><c- o>&lt;</c-><c- n>U</c-><c- o>>></c-></code> is <code class="highlight">false</code> and</p>
    <li data-md>
     <p><code class="highlight"><c- n>conjunction_v</c-><c- o>&lt;</c-><c- n>is_scalar</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-><c- p>,</c-> <c- n>is_same</c-><c- o>&lt;</c-><c- n>T</c-><c- p>,</c-> <c- n>decay_t</c-><c- o>&lt;</c-><c- n>U</c-><c- o>>>></c-></code> is <code class="highlight">false</code>,</p>
    <li data-md>
     <p><code class="highlight"><c- n>is_constructible_v</c-><c- o>&lt;</c-><c- n>T</c-><c- p>,</c-> <c- n>U</c-><c- o>></c-></code> is <code class="highlight">true</code>,</p>
    <li data-md>
     <p><code class="highlight"><c- n>is_assignable_v</c-><c- o>&lt;</c-><c- n>T</c-><c- o>&amp;</c-><c- p>,</c-> <c- n>U</c-><c- o>></c-></code> is <code class="highlight">true</code> and</p>
    <li data-md>
     <p><code class="highlight"><c- n>is_nothrow_move_constructible_v</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code> is <code class="highlight">true</code>.</p>
   </ul>
<pre class="language-c++ highlight"><c- n>template</c-> <c- o>&lt;</c-><c- n>class</c-> <c- n>G</c-> <c- o>=</c-> <c- n>E</c-><c- o>></c->
    <c- n>expected</c-><c- o>&lt;</c-><c- n>T</c-><c- p>,</c-> <c- n>E</c-><c- o>>&amp;</c-> <c- n>operator</c-><c- o>=</c-><c- p>(</c-><c- k>const</c-> <c- n>unexpected</c-><c- o>&lt;</c-><c- n>G</c-><c- o>>&amp;</c-> <c- n>e</c-><c- p>);</c->
</pre>
   <p><em>Effects</em>:</p>
   <p>If <code class="highlight"><c- o>!</c-><c- b>bool</c-><c- p>(</c-><c- o>*</c-><c- k>this</c-><c- p>)</c-></code>, assigns <code class="highlight"><c- n>unexpected</c-><c- p>(</c-><c- n>e</c-><c- p>.</c-><c- n>error</c-><c- p>())</c-></code> to <code class="highlight"><c- n>unexpect</c-></code>;</p>
   <p>otherwise</p>
   <ul>
    <li data-md>
     <p>destroys <code class="highlight"><c- n>val</c-></code> by calling <code class="highlight"><c- n>val</c-><c- p>.</c-><c- o>~</c-><c- n>T</c-><c- p>()</c-></code> if <code class="highlight"><c- n>T</c-></code> is not <code class="highlight"><c- b>void</c-></code>,</p>
    <li data-md>
     <p>initializes <code class="highlight"><c- n>unexpect</c-></code> as if direct-non-list-initializing an object of type <code class="highlight"><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code> with <code class="highlight"><c- n>unexpected</c-><c- p>(</c-><c- n>e</c-><c- p>.</c-><c- n>error</c-><c- p>())</c-></code> and set <code class="highlight"><c- n>has_val</c-></code> to <code class="highlight">false</code>.</p>
   </ul>
   <p><em>Returns</em>: <code class="highlight"><c- o>*</c-><c- k>this</c-></code>.</p>
   <p><em>Postconditions</em>: <code class="highlight"><c- o>!</c-><c- b>bool</c-><c- p>(</c-><c- o>*</c-><c- k>this</c-><c- p>)</c-></code>.</p>
   <p><em>Remarks</em>: If any exception is thrown, <code class="highlight"><c- b>bool</c-><c- p>(</c-><c- o>*</c-><c- k>this</c-><c- p>)</c-></code> remains unchanged.</p>
   <p>This signature shall not participate in overload resolution unless <code class="highlight"><c- n>is_nothrow_copy_constructible_v</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code> is <code class="highlight">true</code> and <code class="highlight"><c- n>is_move_assignable_v</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code> is <code class="highlight">true</code>.</p>
<pre class="language-c++ highlight"><c- n>expected</c-><c- o>&lt;</c-><c- n>T</c-><c- p>,</c-> <c- n>E</c-><c- o>>&amp;</c-> <c- n>operator</c-><c- o>=</c-><c- p>(</c-><c- n>unexpected</c-><c- o>&lt;</c-><c- n>G</c-><c- o>></c-> <c- o>&amp;&amp;</c-> <c- n>e</c-><c- p>);</c->
</pre>
   <p><em>Effects</em>:</p>
   <p>If <code class="highlight"><c- o>!</c-><c- b>bool</c-><c- p>(</c-><c- o>*</c-><c- k>this</c-><c- p>)</c-></code>, move assign <code class="highlight"><c- n>unexpected</c-><c- p>(</c-><c- n>e</c-><c- p>.</c-><c- n>error</c-><c- p>())</c-></code> to <code class="highlight"><c- n>unexpect</c-></code>;</p>
   <p>otherwise</p>
   <ul>
    <li data-md>
     <p>destroys <code class="highlight"><c- n>val</c-></code> by calling <code class="highlight"><c- n>val</c-><c- p>.</c-><c- o>~</c-><c- n>T</c-><c- p>()</c-></code> if <code class="highlight"><c- n>T</c-></code> is not <code class="highlight"><c- b>void</c-></code>,</p>
    <li data-md>
     <p>initializes <code class="highlight"><c- n>unexpect</c-></code> as if direct-non-list-initializing an object of type <code class="highlight"><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code> with <code class="highlight"><c- n>unexpected</c-><c- p>(</c-><c- n>std</c-><c- o>::</c-><c- n>move</c-><c- p>(</c-><c- n>e</c-><c- p>.</c-><c- n>error</c-><c- p>()))</c-></code> and set <code class="highlight"><c- n>has_val</c-></code> to <code class="highlight">false</code>.</p>
   </ul>
   <p><em>Returns</em>: <code class="highlight"><c- o>*</c-><c- k>this</c-></code>.</p>
   <p><em>Postconditions</em>: <code class="highlight"><c- o>!</c-><c- b>bool</c-><c- p>(</c-><c- o>*</c-><c- k>this</c-><c- p>)</c-></code>.</p>
   <p><em>Remarks</em>: If any exception is thrown, <code class="highlight"><c- b>bool</c-><c- p>(</c-><c- o>*</c-><c- k>this</c-><c- p>)</c-></code> remains unchanged.</p>
   <p>This signature shall not participate in overload resolution unless <code class="highlight"><c- n>is_nothrow_move_constructible_v</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code> is <code class="highlight">true</code> and <code class="highlight"><c- n>is_move_assignable_v</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code> is <code class="highlight">true</code>.</p>
<pre class="language-c++ highlight"><c- b>void</c-> <c- n>expected</c-><c- o>&lt;</c-><c- b>void</c-><c- p>,</c-><c- n>E</c-><c- o>>::</c-><c- n>emplace</c-><c- p>();</c->
</pre>
   <p><em>Effects</em>:</p>
   <p>If <code class="highlight"><c- o>!</c-><c- b>bool</c-><c- p>(</c-><c- o>*</c-><c- k>this</c-><c- p>)</c-></code></p>
   <ul>
    <li data-md>
     <p>destroys <code class="highlight"><c- n>unexpect</c-></code> by calling <code class="highlight"><c- n>unexpect</c-><c- p>.</c-><c- o>~</c-><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-><c- p>()</c-></code>,</p>
    <li data-md>
     <p>set <code class="highlight"><c- n>has_val</c-></code> to <code class="highlight">true</code></p>
   </ul>
   <p><em>Postconditions</em>: <code class="highlight"><c- b>bool</c-><c- p>(</c-><c- o>*</c-><c- k>this</c-><c- p>)</c-></code> .</p>
   <p><em>Throws</em>: Nothing</p>
<pre class="language-c++ highlight"><c- n>template</c-> <c- o>&lt;</c-><c- n>class</c-><c- p>...</c-> <c- n>Args</c-><c- o>></c->
    <c- n>T</c-><c- o>&amp;</c-> <c- n>emplace</c-><c- p>(</c-><c- n>Args</c-><c- o>&amp;&amp;</c-><c- p>...</c-> <c- n>args</c-><c- p>);</c->
</pre>
   <p><em>Effects</em>:</p>
   <p>If <code class="highlight"><c- b>bool</c-><c- p>(</c-><c- o>*</c-><c- k>this</c-><c- p>)</c-></code>, assigns <code class="highlight"><c- n>val</c-></code> as if
constructing an object of type <code class="highlight"><c- n>T</c-></code> with the arguments <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>forward</c-><c- o>&lt;</c-><c- n>Args</c-><c- o>></c-><c- p>(</c-><c- n>args</c-><c- p>)...</c-></code></p>
   <p>otherwise if <code class="highlight"><c- n>is_nothrow_constructible_v</c-><c- o>&lt;</c-><c- n>T</c-><c- p>,</c-> <c- n>Args</c-><c- o>&amp;&amp;</c-><c- p>...</c-><c- o>></c-></code> is <code class="highlight">true</code></p>
   <ul>
    <li data-md>
     <p>destroys <code class="highlight"><c- n>unexpect</c-></code> by calling <code class="highlight"><c- n>unexpect</c-><c- p>.</c-><c- o>~</c-><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-><c- p>()</c-></code>,</p>
    <li data-md>
     <p>initializes <code class="highlight"><c- n>val</c-></code> as if direct-non-list-initializing an object of type <code class="highlight"><c- n>T</c-></code> with <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>forward</c-><c- o>&lt;</c-><c- n>Args</c-><c- o>></c-><c- p>(</c-><c- n>args</c-><c- p>)...</c-></code> and</p>
    <li data-md>
     <p>set <code class="highlight"><c- n>has_val</c-></code> to <code class="highlight">true</code>;</p>
   </ul>
   <p>otherwise if <code class="highlight"><c- n>is_nothrow_move_constructible_v</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-></code> is <code class="highlight">true</code></p>
   <ul>
    <li data-md>
     <p>constructs a <code class="highlight"><c- n>T</c-> <c- n>tmp</c-></code> from <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>forward</c-><c- o>&lt;</c-><c- n>Args</c-><c- o>></c-><c- p>(</c-><c- n>args</c-><c- p>)...</c-></code> (which can throw),</p>
    <li data-md>
     <p>destroys <code class="highlight"><c- n>unexpect</c-></code> by calling <code class="highlight"><c- n>unexpect</c-><c- p>.</c-><c- o>~</c-><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-><c- p>()</c-></code>,</p>
    <li data-md>
     <p>initializes <code class="highlight"><c- n>val</c-></code> as if direct-non-list-initializing an object of type <code class="highlight"><c- n>T</c-></code> with <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>move</c-><c- p>(</c-><c- n>tmp</c-><c- p>)</c-></code> (which cannot throw) and</p>
    <li data-md>
     <p>set <code class="highlight"><c- n>has_val</c-></code> to <code class="highlight">true</code>;</p>
   </ul>
   <p>otherwise</p>
   <ul>
    <li data-md>
     <p>move constructs a <code class="highlight"><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-> <c- n>tmp</c-></code> from <code class="highlight"><c- n>unexpected</c-><c- p>(</c-><c- k>this</c-><c- o>-></c-><c- n>error</c-><c- p>())</c-></code> ,</p>
    <li data-md>
     <p>destroys <code class="highlight"><c- n>unexpect</c-></code> by calling <code class="highlight"><c- n>unexpect</c-><c- p>.</c-><c- o>~</c-><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-><c- p>()</c-></code>,</p>
    <li data-md>
     <p>initializes <code class="highlight"><c- n>val</c-></code> as if direct-non-list-initializing an object of type <code class="highlight"><c- n>T</c-></code> with <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>forward</c-><c- o>&lt;</c-><c- n>Args</c-><c- o>></c-><c- p>(</c-><c- n>args</c-><c- p>)...</c-></code>. Either,</p>
     <ul>
      <li data-md>
       <p>the constructor didn’t throw, set <code class="highlight"><c- n>has_val</c-></code> to <code class="highlight">true</code>, or</p>
      <li data-md>
       <p>the constructor did throw, so move-construct the <code class="highlight"><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code> from <code class="highlight"><c- n>tmp</c-></code> back into the expected storage (which can’t throw as <code class="highlight"><c- n>E</c-></code> is nothrow-move-constructible), and re-throw the exception.</p>
     </ul>
   </ul>
   <p><em>Postconditions</em>: <code class="highlight"><c- b>bool</c-><c- p>(</c-><c- o>*</c-><c- k>this</c-><c- p>)</c-></code> .</p>
   <p><em>Returns:</em> A reference to the new contained value <code class="highlight"><c- n>val</c-></code>.</p>
   <p><em>Throws</em>: Any exception thrown by the operations specified in the effect clause.</p>
   <p><em>Remarks</em>: If an exception is thrown during the call to <code class="highlight"><c- n>T</c-></code>'s assignment, nothing
changes.</p>
   <p>This signature shall not participate in overload resolution unless: <code class="highlight"><c- n>T</c-></code> is not <code class="highlight"><c- b>void</c-></code> and <code class="highlight"><c- n>is_nothrow_constructible_v</c-><c- o>&lt;</c-><c- n>T</c-><c- p>,</c-> <c- n>Args</c-><c- o>&amp;&amp;</c-><c- p>...</c-><c- o>></c-></code> is <code class="highlight">true</code>.</p>
<pre class="language-c++ highlight"><c- n>template</c-> <c- o>&lt;</c-><c- n>class</c-> <c- n>U</c-><c- p>,</c-> <c- n>class</c-><c- p>...</c-> <c- n>Args</c-><c- o>></c->
    <c- n>T</c-><c- o>&amp;</c-> <c- n>emplace</c-><c- p>(</c-><c- n>initializer_list</c-><c- o>&lt;</c-><c- n>U</c-><c- o>></c-> <c- n>il</c-><c- p>,</c-> <c- n>Args</c-><c- o>&amp;&amp;</c-><c- p>...</c-> <c- n>args</c-><c- p>);</c->
</pre>
   <p><em>Effects</em>:</p>
   <p>If <code class="highlight"><c- b>bool</c-><c- p>(</c-><c- o>*</c-><c- k>this</c-><c- p>)</c-></code>, assigns <code class="highlight"><c- n>val</c-></code> as if
constructing an object of type <code class="highlight"><c- n>T</c-></code> with the arguments <code class="highlight"><c- n>il</c-><c- p>,</c-> <c- n>std</c-><c- o>::</c-><c- n>forward</c-><c- o>&lt;</c-><c- n>Args</c-><c- o>></c-><c- p>(</c-><c- n>args</c-><c- p>)...</c-></code></p>
   <p>otherwise if <code class="highlight"><c- n>is_nothrow_constructible_v</c-><c- o>&lt;</c-><c- n>T</c-><c- p>,</c-> <c- n>initializer_list</c-><c- o>&lt;</c-><c- n>U</c-><c- o>>&amp;</c-><c- p>,</c-> <c- n>Args</c-><c- o>&amp;&amp;</c-><c- p>...</c-><c- o>></c-></code> is <code class="highlight">true</code></p>
   <ul>
    <li data-md>
     <p>destroys <code class="highlight"><c- n>unexpect</c-></code> by calling <code class="highlight"><c- n>unexpect</c-><c- p>.</c-><c- o>~</c-><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-><c- p>()</c-></code>,</p>
    <li data-md>
     <p>initializes <code class="highlight"><c- n>val</c-></code> as if direct-non-list-initializing an object of type <code class="highlight"><c- n>T</c-></code> with <code class="highlight"><c- n>il</c-><c- p>,</c-> <c- n>std</c-><c- o>::</c-><c- n>forward</c-><c- o>&lt;</c-><c- n>Args</c-><c- o>></c-><c- p>(</c-><c- n>args</c-><c- p>)...</c-></code> and</p>
    <li data-md>
     <p>set <code class="highlight"><c- n>has_val</c-></code> to <code class="highlight">true</code>;</p>
   </ul>
   <p>otherwise if <code class="highlight"><c- n>is_nothrow_move_constructible_v</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-></code> is <code class="highlight">true</code></p>
   <ul>
    <li data-md>
     <p>constructs a <code class="highlight"><c- n>T</c-> <c- n>tmp</c-></code> from <code class="highlight"><c- n>il</c-><c- p>,</c-> <c- n>std</c-><c- o>::</c-><c- n>forward</c-><c- o>&lt;</c-><c- n>Args</c-><c- o>></c-><c- p>(</c-><c- n>args</c-><c- p>)...</c-></code> (which can throw),</p>
    <li data-md>
     <p>destroys <code class="highlight"><c- n>unexpect</c-></code> by calling <code class="highlight"><c- n>unexpect</c-><c- p>.</c-><c- o>~</c-><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-><c- p>()</c-></code>,</p>
    <li data-md>
     <p>initializes <code class="highlight"><c- n>val</c-></code> as if direct-non-list-initializing an object of type <code class="highlight"><c- n>T</c-></code> with <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>move</c-><c- p>(</c-><c- n>tmp</c-><c- p>)</c-></code> (which cannot throw) and</p>
    <li data-md>
     <p>set <code class="highlight"><c- n>has_val</c-></code> to <code class="highlight">true</code>;</p>
   </ul>
   <p>otherwise</p>
   <ul>
    <li data-md>
     <p>move constructs a <code class="highlight"><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-> <c- n>tmp</c-></code> from <code class="highlight"><c- n>unexpected</c-><c- p>(</c-><c- k>this</c-><c- o>-></c-><c- n>error</c-><c- p>())</c-></code> ,</p>
    <li data-md>
     <p>destroys <code class="highlight"><c- n>unexpect</c-></code> by calling <code class="highlight"><c- n>unexpect</c-><c- p>.</c-><c- o>~</c-><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-><c- p>()</c-></code>,</p>
    <li data-md>
     <p>initializes <code class="highlight"><c- n>val</c-></code> as if direct-non-list-initializing an object of type <code class="highlight"><c- n>T</c-></code> with <code class="highlight"><c- n>il</c-><c- p>,</c-> <c- n>std</c-><c- o>::</c-><c- n>forward</c-><c- o>&lt;</c-><c- n>Args</c-><c- o>></c-><c- p>(</c-><c- n>args</c-><c- p>)...</c-></code>. Either,</p>
     <ul>
      <li data-md>
       <p>the constructor didn’t throw, set <code class="highlight"><c- n>has_val</c-></code> to <code class="highlight">true</code>, or</p>
      <li data-md>
       <p>the constructor did throw, so move-construct the <code class="highlight"><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code> from <code class="highlight"><c- n>tmp</c-></code> back into the expected storage (which can’t throw as <code class="highlight"><c- n>E</c-></code> is nothrow-move-constructible), and re-throw the exception.</p>
     </ul>
   </ul>
   <p><em>Postconditions</em>: <code class="highlight"><c- b>bool</c-><c- p>(</c-><c- o>*</c-><c- k>this</c-><c- p>)</c-></code> .</p>
   <p><em>Returns:</em> A reference to the new contained value <code class="highlight"><c- n>val</c-></code>.</p>
   <p><em>Throws</em>: Any exception thrown by the operations specified in the effect clause.</p>
   <p><em>Remarks</em>: If an exception is thrown during the call to <code class="highlight"><c- n>T</c-></code>'s assignment nothing
changes.</p>
   <p>The function shall not participate in overload resolution unless: <code class="highlight"><c- n>T</c-></code> is not <code class="highlight"><c- b>void</c-></code> and <code class="highlight"><c- n>is_nothrow_constructible_v</c-><c- o>&lt;</c-><c- n>T</c-><c- p>,</c-> <c- n>initializer_list</c-><c- o>&lt;</c-><c- n>U</c-><c- o>>&amp;</c-><c- p>,</c-> <c- n>Args</c-><c- o>&amp;&amp;</c-><c- p>...</c-><c- o>></c-></code> is <code class="highlight">true</code>.</p>
   <h3 class="heading settled" data-level="1.9" id="expected.object.swap"><span class="secno">1.9. </span><span class="content">�.�.4.4 Swap [<em>expected.object.swap</em>]</span><a class="self-link" href="#expected.object.swap"></a></h3>
<pre class="language-c++ highlight"><c- b>void</c-> <c- nf>swap</c-><c- p>(</c-><c- n>expected</c-><c- o>&lt;</c-><c- n>T</c-><c- p>,</c-> <c- n>E</c-><c- o>>&amp;</c-> <c- n>rhs</c-><c- p>)</c-> <c- n>noexcept</c-><c- p>(</c-><c- n>see</c-> <c- n>below</c-><c- p>);</c->
</pre>
   <p><em>Effects</em>: if <code class="highlight"><c- b>bool</c-><c- p>(</c-><c- o>*</c-><c- k>this</c-><c- p>)</c-></code> and <code class="highlight"><c- b>bool</c-><c- p>(</c-><c- n>rhs</c-><c- p>)</c-></code>,</p>
   <ul>
    <li data-md>
     <p>if <code class="highlight"><c- n>T</c-></code> is not <code class="highlight"><c- b>void</c-></code> calls <code class="highlight"><c- k>using</c-> <c- n>std</c-><c- o>::</c-><c- n>swap</c-><c- p>;</c-> <c- n>swap</c-><c- p>(</c-><c- n>val</c-><c- p>,</c-> <c- n>rhs</c-><c- p>.</c-><c- n>val</c-><c- p>)</c-></code>,</p>
   </ul>
   <p>otherwise if <code class="highlight"><c- o>!</c-><c- b>bool</c-><c- p>(</c-><c- o>*</c-><c- k>this</c-><c- p>)</c-></code> and <code class="highlight"><c- o>!</c-><c- b>bool</c-><c- p>(</c-><c- n>rhs</c-><c- p>)</c-></code>,</p>
   <ul>
    <li data-md>
     <p>calls <code class="highlight"><c- k>using</c-> <c- n>std</c-><c- o>::</c-><c- n>swap</c-><c- p>;</c-> <c- n>swap</c-><c- p>(</c-><c- n>unexpect</c-><c- p>,</c-> <c- n>rhs</c-><c- p>.</c-><c- n>unexpect</c-><c- p>)</c-></code>,</p>
   </ul>
   <p>otherwise if <code class="highlight"><c- o>!</c-><c- b>bool</c-><c- p>(</c-><c- o>*</c-><c- k>this</c-><c- p>)</c-></code> and <code class="highlight"><c- b>bool</c-><c- p>(</c-><c- n>rhs</c-><c- p>)</c-></code>,</p>
   <ul>
    <li data-md>
     <p>calls <code class="highlight"><c- n>rhs</c-><c- p>.</c-><c- n>swap</c-><c- p>(</c-><c- o>*</c-><c- k>this</c-><c- p>)</c-></code>,</p>
   </ul>
   <p>otherwise</p>
   <ul>
    <li data-md>
     <p>if <code class="highlight"><c- n>T</c-></code> is <code class="highlight"><c- b>void</c-></code></p>
     <ul>
      <li data-md>
       <p>initializes <code class="highlight"><c- n>unexpect</c-></code> as if direct-non-list-initializing an object of type <code class="highlight"><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code> with <code class="highlight"><c- n>unexpected</c-><c- p>(</c-><c- n>std</c-><c- o>::</c-><c- n>move</c-><c- p>(</c-><c- n>rhs</c-><c- p>))</c-></code>. Either</p>
      <li data-md>
       <p>the constructor didn’t throw, set <code class="highlight"><c- n>has_val</c-></code> to <code class="highlight">false</code>, destroys <code class="highlight"><c- n>rhs</c-><c- p>.</c-><c- n>unexpect</c-></code> by calling <code class="highlight"><c- n>rhs</c-><c- p>.</c-><c- n>unexpect</c-><c- p>.</c-><c- o>~</c-><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-><c- p>()</c-></code> set <code class="highlight"><c- n>rhs</c-><c- p>.</c-><c- n>has_val</c-></code> to <code class="highlight">true</code>.</p>
      <li data-md>
       <p>the constructor did throw, rethrow the exception.</p>
     </ul>
    <li data-md>
     <p>otherwise if <code class="highlight"><c- n>is_nothrow_move_constructible_v</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code> is <code class="highlight">true</code>,</p>
     <ul>
      <li data-md>
       <p>the <code class="highlight"><c- n>unexpect</c-></code> of <code class="highlight"><c- n>rhs</c-></code> is moved to a temporary variable <code class="highlight"><c- n>tmp</c-></code> of type <code class="highlight"><c- n>unexpected_type</c-></code>,</p>
      <li data-md>
       <p>followed by destruction of <code class="highlight"><c- n>unexpect</c-></code> as if by <code class="highlight"><c- n>rhs</c-><c- p>.</c-><c- n>unexpect</c-><c- p>.</c-><c- o>~</c-><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-><c- p>()</c-></code>,</p>
      <li data-md>
       <p><code class="highlight"><c- n>rhs</c-><c- p>.</c-><c- n>val</c-></code> is direct-initialized from <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>move</c-><c- p>(</c-><c- o>*</c-><c- k>this</c-><c- p>)</c-></code>. Either</p>
       <ul>
        <li data-md>
         <p>the constructor didn’t throw</p>
         <ul>
          <li data-md>
           <p>destroy <code class="highlight"><c- n>val</c-></code> as if by <code class="highlight"><c- k>this</c-><c- o>-></c-><c- n>val</c-><c- p>.</c-><c- o>~</c-><c- n>T</c-><c- p>()</c-></code>,</p>
          <li data-md>
           <p>the <code class="highlight"><c- n>unexpect</c-></code> of <code class="highlight"><c- k>this</c-></code> is direct-initialized from <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>move</c-><c- p>(</c-><c- n>tmp</c-><c- p>)</c-></code>, after this, <code class="highlight"><c- k>this</c-></code> does not contain a value; and <code class="highlight"><c- b>bool</c-><c- p>(</c-><c- n>rhs</c-><c- p>)</c-></code>.</p>
         </ul>
        <li data-md>
         <p>the constructor did throw, so move-construct the <code class="highlight"><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code> from <code class="highlight"><c- n>tmp</c-></code> back into the expected storage (which can’t throw as <code class="highlight"><c- n>E</c-></code> is nothrow-move-constructible), and re-throw the exception.</p>
       </ul>
     </ul>
    <li data-md>
     <p>otherwise if <code class="highlight"><c- n>is_nothrow_move_constructible_v</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-></code> is <code class="highlight">true</code>,</p>
     <ul>
      <li data-md>
       <p><code class="highlight"><c- n>val</c-></code> is moved to a temporary variable <code class="highlight"><c- n>tmp</c-></code> of type <code class="highlight"><c- n>T</c-></code>,</p>
      <li data-md>
       <p>followed by destruction of <code class="highlight"><c- n>val</c-></code> as if by <code class="highlight"><c- n>val</c-><c- p>.</c-><c- o>~</c-><c- n>T</c-><c- p>()</c-></code>,</p>
      <li data-md>
       <p>the <code class="highlight"><c- n>unexpect</c-></code> is direct-initialized from <code class="highlight"><c- n>unexpected</c-><c- p>(</c-><c- n>std</c-><c- o>::</c-><c- n>move</c-><c- p>(</c-><c- n>other</c-><c- p>.</c-><c- n>error</c-><c- p>()))</c-></code>. Either</p>
       <ul>
        <li data-md>
         <p>the constructor didn’t throw</p>
         <ul>
          <li data-md>
           <p>destroy <code class="highlight"><c- n>rhs</c-><c- p>.</c-><c- n>unexpect</c-></code> as if by <code class="highlight"><c- n>rhs</c-><c- p>.</c-><c- n>unexpect</c-><c- p>.</c-><c- o>~</c-><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-><c- p>()</c-></code>,</p>
          <li data-md>
           <p><code class="highlight"><c- n>rhs</c-><c- p>.</c-><c- n>val</c-></code> is direct-initialized from <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>move</c-><c- p>(</c-><c- n>tmp</c-><c- p>)</c-></code>, after this, <code class="highlight"><c- k>this</c-></code> does not contain a value; and <code class="highlight"><c- b>bool</c-><c- p>(</c-><c- n>rhs</c-><c- p>)</c-></code>.</p>
         </ul>
        <li data-md>
         <p>the constructor did throw, so move-construct the <code class="highlight"><c- n>T</c-></code> from <code class="highlight"><c- n>tmp</c-></code> back into the expected storage (which can’t throw as <code class="highlight"><c- n>T</c-></code> is nothrow-move-constructible), and re-throw the exception.</p>
       </ul>
     </ul>
    <li data-md>
     <p>otherwise, the function is not defined.</p>
   </ul>
   <p><em>Throws</em>: Any exceptions that the expressions in the Effects clause throw.</p>
   <p><em>Remarks</em>: The expression inside noexcept is equivalent to: <code class="highlight"><c- n>is_nothrow_move_constructible_v</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-></code> is <code class="highlight">true</code> and <code class="highlight"><c- n>is_nothrow_swappable_v</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-></code> is <code class="highlight">true</code> and <code class="highlight"><c- n>is_nothrow_move_constructible_v</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code> is <code class="highlight">true</code> and <code class="highlight"><c- n>is_nothrow_swappable_v</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code> is <code class="highlight">true</code>.
 The function shall not
participate in overload resolution unless:</p>
   <ul>
    <li data-md>
     <p>Lvalues of type <code class="highlight"><c- n>T</c-></code> shall be <code class="highlight"><c- n>Swappable</c-></code>,</p>
    <li data-md>
     <p>Lvalues of type <code class="highlight"><c- n>E</c-></code> shall be <code class="highlight"><c- n>Swappable</c-></code>,</p>
    <li data-md>
     <p><code class="highlight"><c- n>is_void_v</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-></code> is <code class="highlight">true</code> or</p>
    <li data-md>
     <p><code class="highlight"><c- n>is_void_v</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-></code> is <code class="highlight">false</code> and</p>
     <ul>
      <li data-md>
       <p><code class="highlight"><c- n>is_move_constructible_v</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-></code> is <code class="highlight">true</code>,</p>
      <li data-md>
       <p><code class="highlight"><c- n>is_move_constructible_v</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code> is <code class="highlight">true</code> and</p>
      <li data-md>
       <p><code class="highlight"><c- n>is_move_constructible_v</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code> is <code class="highlight">true</code> or <code class="highlight"><c- n>is_move_constructible_v</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-></code> is <code class="highlight">true</code>.</p>
     </ul>
   </ul>
   <h3 class="heading settled" data-level="1.10" id="expected.object.observe"><span class="secno">1.10. </span><span class="content">�.�.4.5 Observers [<em>expected.object.observe</em>]</span><a class="self-link" href="#expected.object.observe"></a></h3>
<pre class="language-c++ highlight"><c- n>constexpr</c-> <c- k>const</c-> <c- n>T</c-><c- o>*</c-> <c- n>operator</c-><c- o>-></c-><c- p>()</c-> <c- k>const</c-><c- p>;</c->
<c- n>T</c-><c- o>*</c-> <c- n>operator</c-><c- o>-></c-><c- p>();</c->
</pre>
   <p><em>Requires</em>: <code class="highlight"><c- b>bool</c-><c- p>(</c-><c- o>*</c-><c- k>this</c-><c- p>)</c-></code> .</p>
   <p><em>Returns</em>: <code class="highlight"><c- n>addressof</c-><c- p>(</c-><c- n>val</c-><c- p>)</c-></code>.</p>
   <p><em>Remarks</em>: Unless <code class="highlight"><c- n>T</c-></code> is a user-defined type with overloaded unary <code class="highlight"><c- k>operator</c-><c- o>&amp;</c-></code>,
the first operator shall be a constexpr function.
The operator shall not participate in overload resolution unless: <code class="highlight"><c- n>T</c-></code> is not <code class="highlight"><c- b>void</c-></code>.</p>
<pre class="language-c++ highlight"><c- n>constexpr</c-> <c- k>const</c-> <c- n>T</c-><c- o>&amp;</c-> <c- n>operator</c-> <c- o>*</c-><c- p>()</c-> <c- k>const</c-><c- o>&amp;</c-><c- p>;</c->
<c- n>T</c-><c- o>&amp;</c-> <c- n>operator</c-> <c- o>*</c-><c- p>()</c-> <c- o>&amp;</c-><c- p>;</c->
</pre>
   <p><em>Requires</em>: <code class="highlight"><c- b>bool</c-><c- p>(</c-><c- o>*</c-><c- k>this</c-><c- p>)</c-></code> .</p>
   <p><em>Returns</em>: <code class="highlight"><c- n>val</c-></code>.</p>
   <p><em>Remarks</em>: The first operator shall be a constexpr function.
The operator shall not participate in overload resolution unless: <code class="highlight"><c- n>T</c-></code> is not <code class="highlight"><c- b>void</c-></code>.</p>
<pre class="language-c++ highlight"><c- n>constexpr</c-> <c- n>T</c-><c- o>&amp;&amp;</c-> <c- n>operator</c-> <c- o>*</c-><c- p>()</c-> <c- o>&amp;&amp;</c-><c- p>;</c->
<c- n>constexpr</c-> <c- k>const</c-> <c- n>T</c-><c- o>&amp;&amp;</c-> <c- n>operator</c-> <c- o>*</c-><c- p>()</c-> <c- k>const</c-><c- o>&amp;&amp;</c-><c- p>;</c->
</pre>
   <p><em>Requires</em>: <code class="highlight"><c- b>bool</c-><c- p>(</c-><c- o>*</c-><c- k>this</c-><c- p>)</c-></code> .</p>
   <p><em>Returns</em>: <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>move</c-><c- p>(</c-><c- n>val</c-><c- p>)</c-></code>.</p>
   <p><em>Remarks</em>: This operator shall be a constexpr function.
The operator shall not participate in overload resolution unless: <code class="highlight"><c- n>T</c-></code> is not <code class="highlight"><c- b>void</c-></code>.</p>
<pre class="language-c++ highlight"><c- n>constexpr</c-> <c- n>explicit</c-> <c- n>operator</c-> <c- nf>bool</c-><c- p>()</c-> <c- n>noexcept</c-><c- p>;</c->
</pre>
   <p><em>Returns</em>: <code class="highlight"><c- n>has_val</c-></code>.</p>
   <p><em>Remarks</em>: This operator shall be a constexpr function.</p>
<pre class="language-c++ highlight"><c- n>constexpr</c-> <c- b>bool</c-> <c- nf>has_value</c-><c- p>()</c-> <c- k>const</c-> <c- n>noexcept</c-><c- p>;</c->
</pre>
   <p><em>Returns</em>: <code class="highlight"><c- n>has_val</c-></code>.</p>
   <p><em>Remarks</em>: This function shall be a constexpr function.</p>
<pre class="language-c++ highlight"><c- n>constexpr</c-> <c- b>void</c-> <c- n>expected</c-><c- o>&lt;</c-><c- b>void</c-><c- p>,</c-> <c- n>E</c-><c- o>>::</c-><c- n>value</c-><c- p>()</c-> <c- k>const</c-><c- p>;</c->
</pre>
   <p><em>Throws</em>: <code class="highlight"><c- n>bad_expected_access</c-><c- p>(</c-><c- n>error</c-><c- p>())</c-></code> if <code class="highlight"><c- o>!</c-><c- b>bool</c-><c- p>(</c-><c- o>*</c-><c- k>this</c-><c- p>)</c-></code>.</p>
<pre class="language-c++ highlight"><c- n>constexpr</c-> <c- k>const</c-> <c- n>T</c-><c- o>&amp;</c-> <c- n>expected</c-><c- o>::</c-><c- n>value</c-><c- p>()</c-> <c- k>const</c-><c- o>&amp;</c-><c- p>;</c->
<c- n>constexpr</c-> <c- n>T</c-><c- o>&amp;</c-> <c- n>expected</c-><c- o>::</c-><c- n>value</c-><c- p>()</c-> <c- o>&amp;</c-><c- p>;</c->
</pre>
   <p><em>Returns</em>: <code class="highlight"><c- n>val</c-></code>, if <code class="highlight"><c- b>bool</c-><c- p>(</c-><c- o>*</c-><c- k>this</c-><c- p>)</c-></code> .</p>
   <p><em>Throws</em>: <code class="highlight"><c- n>bad_expected_access</c-><c- p>(</c-><c- n>error</c-><c- p>())</c-></code> if <code class="highlight"><c- o>!</c-><c- b>bool</c-><c- p>(</c-><c- o>*</c-><c- k>this</c-><c- p>)</c-></code>.</p>
   <p><em>Remarks</em>: These functions shall be constexpr functions.
The operator shall not participate in overload resolution unless: <code class="highlight"><c- n>T</c-></code> is not <code class="highlight"><c- b>void</c-></code>.</p>
<pre class="language-c++ highlight"><c- n>constexpr</c-> <c- n>T</c-><c- o>&amp;&amp;</c-> <c- n>expected</c-><c- o>::</c-><c- n>value</c-><c- p>()</c-> <c- o>&amp;&amp;</c-><c- p>;</c->
<c- n>constexpr</c-> <c- k>const</c-> <c- n>T</c-><c- o>&amp;&amp;</c-> <c- n>expected</c-><c- o>::</c-><c- n>value</c-><c- p>()</c-> <c- k>const</c-><c- o>&amp;&amp;</c-><c- p>;</c->
</pre>
   <p><em>Returns</em>: <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>move</c-><c- p>(</c-><c- n>val</c-><c- p>)</c-></code>, if <code class="highlight"><c- b>bool</c-><c- p>(</c-><c- o>*</c-><c- k>this</c-><c- p>)</c-></code> .</p>
   <p><em>Throws</em>: <code class="highlight"><c- n>bad_expected_access</c-><c- p>(</c-><c- n>error</c-><c- p>())</c-></code> if <code class="highlight"><c- o>!</c-><c- b>bool</c-><c- p>(</c-><c- o>*</c-><c- k>this</c-><c- p>)</c-></code>.</p>
   <p><em>Remarks</em>: These functions shall be constexpr functions.
The operator shall not participate in overload resolution unless: <code class="highlight"><c- n>T</c-></code> is not <code class="highlight"><c- b>void</c-></code>.</p>
<pre class="language-c++ highlight"><c- n>constexpr</c-> <c- k>const</c-> <c- n>E</c-><c- o>&amp;</c-> <c- n>error</c-><c- p>()</c-> <c- k>const</c-><c- o>&amp;</c-><c- p>;</c->
<c- n>constexpr</c-> <c- n>E</c-><c- o>&amp;</c-> <c- n>error</c-><c- p>()</c-> <c- o>&amp;</c-><c- p>;</c->
</pre>
   <p><em>Requires</em>: <code class="highlight"><c- o>!</c-><c- b>bool</c-><c- p>(</c-><c- o>*</c-><c- k>this</c-><c- p>)</c-></code>.</p>
   <p><em>Returns</em>: <code class="highlight"><c- n>unexpect</c-><c- p>.</c-><c- n>value</c-><c- p>()</c-></code>.</p>
   <p><em>Remarks</em>: The first function shall be a constexpr function.</p>
<pre class="language-c++ highlight"><c- n>constexpr</c-> <c- n>E</c-><c- o>&amp;&amp;</c-> <c- n>error</c-><c- p>()</c-> <c- o>&amp;&amp;</c-><c- p>;</c->
<c- n>constexpr</c-> <c- k>const</c-> <c- n>E</c-><c- o>&amp;&amp;</c-> <c- n>error</c-><c- p>()</c-> <c- k>const</c-> <c- o>&amp;&amp;</c-><c- p>;</c->
</pre>
   <p><em>Requires</em>: <code class="highlight"><c- o>!</c-><c- b>bool</c-><c- p>(</c-><c- o>*</c-><c- k>this</c-><c- p>)</c-></code>.</p>
   <p><em>Returns</em>: <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>move</c-><c- p>(</c-><c- n>unexpect</c-><c- p>.</c-><c- n>value</c-><c- p>())</c-></code>.</p>
   <p><em>Remarks</em>: The first function shall be a constexpr function.</p>
<pre class="language-c++ highlight"><c- n>template</c-> <c- o>&lt;</c-><c- n>class</c-> <c- n>U</c-><c- o>></c->
    <c- n>constexpr</c-> <c- n>T</c-> <c- n>value_or</c-><c- p>(</c-><c- n>U</c-><c- o>&amp;&amp;</c-> <c- n>v</c-><c- p>)</c-> <c- k>const</c-><c- o>&amp;</c-><c- p>;</c->
</pre>
   <p><em>Returns</em>: <code class="highlight"><c- b>bool</c-><c- p>(</c-><c- o>*</c-><c- k>this</c-><c- p>)</c-> <c- o>?</c-> <c- o>**</c-><c- k>this</c-> <c- o>:</c-> <c- k>static_cast</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-><c- p>(</c-><c- n>std</c-><c- o>::</c-><c- n>forward</c-><c- o>&lt;</c-><c- n>U</c-><c- o>></c-><c- p>(</c-><c- n>v</c-><c- p>));</c-></code>.</p>
   <p><em>Remarks</em>: If <code class="highlight"><c- n>is_copy_constructible_v</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-> <c- n>is</c-></code><code class="highlight" data-span-tag="true"> <c- o>&amp;&amp;</c-> <c- n>is_convertible_v</c-><c- o>&lt;</c-><c- n>U</c-><c- o>&amp;&amp;</c-><c- p>,</c-> <c- n>T</c-><c- o>></c-></code> is <code class="highlight">false</code> the program is ill-formed.</p>
<pre class="language-c++ highlight"><c- n>template</c-> <c- o>&lt;</c-><c- n>class</c-> <c- n>U</c-><c- o>></c->
    <c- n>constexpr</c-> <c- n>T</c-> <c- n>value_or</c-><c- p>(</c-><c- n>U</c-><c- o>&amp;&amp;</c-> <c- n>v</c-><c- p>)</c-> <c- o>&amp;&amp;</c-><c- p>;</c->
</pre>
   <p><em>Returns</em>: <code class="highlight"><c- b>bool</c-><c- p>(</c-><c- o>*</c-><c- k>this</c-><c- p>)</c-> <c- o>?</c-> <c- n>std</c-><c- o>::</c-><c- n>move</c-><c- p>(</c-><c- o>**</c-><c- k>this</c-><c- p>)</c-> <c- o>:</c-> <c- k>static_cast</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-><c- p>(</c-><c- n>std</c-><c- o>::</c-><c- n>forward</c-><c- o>&lt;</c-><c- n>U</c-><c- o>></c-><c- p>(</c-><c- n>v</c-><c- p>));</c-></code>.</p>
   <p><em>Remarks</em>: If <code class="highlight"><c- n>is_move_constructible_v</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-></code> is <code class="highlight">true</code> and <code class="highlight"><c- n>is_convertible_v</c-><c- o>&lt;</c-><c- n>U</c-><c- o>&amp;&amp;</c-><c- p>,</c-> <c- n>T</c-><c- o>></c-></code> is <code class="highlight">false</code> the program is ill-formed.</p>
   <h3 class="heading settled" data-level="1.11" id="expected.equality_op"><span class="secno">1.11. </span><span class="content">�.�.4.6 Expected Equality operators [<em>expected.equality_op</em>]</span><a class="self-link" href="#expected.equality_op"></a></h3>
<pre class="language-c++ highlight"><c- n>template</c-> <c- o>&lt;</c-><c- n>class</c-> <c- n>T1</c-><c- p>,</c-> <c- n>class</c-> <c- n>E1</c-><c- p>,</c-> <c- n>class</c-> <c- n>T2</c-><c- p>,</c-> <c- n>class</c-> <c- n>E2</c-><c- o>></c->
    <c- n>friend</c-> <c- n>constexpr</c-> <c- b>bool</c-> <c- n>operator</c-><c- o>==</c-><c- p>(</c-><c- k>const</c-> <c- n>expected</c-><c- o>&lt;</c-><c- n>T1</c-><c- p>,</c-> <c- n>E1</c-><c- o>>&amp;</c-> <c- n>x</c-><c- p>,</c-> <c- k>const</c-> <c- n>expected</c-><c- o>&lt;</c-><c- n>T2</c-><c- p>,</c-> <c- n>E2</c-><c- o>>&amp;</c-> <c- n>y</c-><c- p>);</c->
</pre>
   <p><em>Requires</em>: The expressions <code class="highlight"><c- o>*</c-><c- n>x</c-> <c- o>==</c-> <c- o>*</c-><c- n>y</c-></code> and <code class="highlight"><c- n>unexpected</c-><c- p>(</c-><c- n>x</c-><c- p>.</c-><c- n>error</c-><c- p>())</c-> <c- o>==</c-> <c- n>unexpected</c-><c- p>(</c-><c- n>y</c-><c- p>.</c-><c- n>error</c-><c- p>())</c-></code> shall be well-formed and its result
shall be convertible to <code class="highlight"><c- b>bool</c-></code>.</p>
   <p><em>Returns</em>: If <code class="highlight"><c- b>bool</c-><c- p>(</c-><c- n>x</c-><c- p>)</c-> <c- o>!=</c-> <c- b>bool</c-><c- p>(</c-><c- n>y</c-><c- p>)</c-></code>, <code class="highlight">false</code>; otherwise if <code class="highlight"><c- b>bool</c-><c- p>(</c-><c- n>x</c-><c- p>)</c-> <c- o>==</c-> false</code>, <code class="highlight"><c- n>x</c-><c- p>.</c-><c- n>error</c-><c- p>()</c-> <c- o>==</c-> <c- n>y</c-><c- p>.</c-><c- n>error</c-><c- p>()</c-></code>; otherwise <code class="highlight">true</code> if <code class="highlight"><c- n>T1</c-></code> and <code class="highlight"><c- n>T2</c-></code> are <code class="highlight"><c- b>void</c-></code> or <code class="highlight"><c- o>*</c-><c- n>x</c-> <c- o>==</c-> <c- o>*</c-><c- n>y</c-></code> otherwise.</p>
   <p><em>Remarks</em>: Specializations of this function template, for which <code class="highlight"><c- n>T1</c-></code> and <code class="highlight"><c- n>T2</c-></code> are <code class="highlight"><c- b>void</c-></code> or <code class="highlight"><c- o>*</c-><c- n>x</c-> <c- o>==</c-> <c- o>*</c-><c- n>y</c-></code> and <code class="highlight"><c- n>x</c-><c- p>.</c-><c- n>error</c-><c- p>()</c-> <c- o>==</c-> <c- n>y</c-><c- p>.</c-><c- n>error</c-><c- p>()</c-></code> are core constant expression, shall be <code class="highlight"><c- k>constexpr</c-></code> functions.</p>
<pre class="language-c++ highlight"><c- n>template</c-> <c- o>&lt;</c-><c- n>class</c-> <c- n>T1</c-><c- p>,</c-> <c- n>class</c-> <c- n>E1</c-><c- p>,</c-> <c- n>class</c-> <c- n>T2</c-><c- p>,</c-> <c- n>class</c-> <c- n>E2</c-><c- o>></c->
    <c- n>constexpr</c-> <c- b>bool</c-> <c- n>operator</c-><c- o>!=</c-><c- p>(</c-><c- k>const</c-> <c- n>expected</c-><c- o>&lt;</c-><c- n>T1</c-><c- p>,</c-> <c- n>E1</c-><c- o>>&amp;</c-> <c- n>x</c-><c- p>,</c-> <c- k>const</c-> <c- n>expected</c-><c- o>&lt;</c-><c- n>T2</c-><c- p>,</c-> <c- n>E2</c-><c- o>>&amp;</c-> <c- n>y</c-><c- p>);</c->
</pre>
   <p><em>Requires</em>: The expressions <code class="highlight"><c- o>*</c-><c- n>x</c-> <c- o>!=</c-> <c- o>*</c-><c- n>y</c-></code> and <code class="highlight"><c- n>x</c-><c- p>.</c-><c- n>error</c-><c- p>()</c-> <c- o>!=</c-> <c- n>y</c-><c- p>.</c-><c- n>error</c-><c- p>()</c-></code> shall be
well-formed and its result shall be convertible to <code class="highlight"><c- b>bool</c-></code>.</p>
   <p><em>Returns</em>: If <code class="highlight"><c- b>bool</c-><c- p>(</c-><c- n>x</c-><c- p>)</c-> <c- o>!=</c-> <c- b>bool</c-><c- p>(</c-><c- n>y</c-><c- p>)</c-></code>, <code class="highlight">true</code>; otherwise if <code class="highlight"><c- b>bool</c-><c- p>(</c-><c- n>x</c-><c- p>)</c-> <c- o>==</c-> false</code>, <code class="highlight"><c- n>x</c-><c- p>.</c-><c- n>error</c-><c- p>()</c-> <c- o>!=</c-> <c- n>y</c-><c- p>.</c-><c- n>error</c-><c- p>()</c-></code>; otherwise <code class="highlight">true</code> if <code class="highlight"><c- n>T1</c-></code> and <code class="highlight"><c- n>T2</c-></code> are <code class="highlight"><c- b>void</c-></code> or <code class="highlight"><c- o>*</c-><c- n>x</c-> <c- o>!=</c-> <c- o>*</c-><c- n>y</c-></code>.</p>
   <p><em>Remarks</em>: Specializations of this function template, for which <code class="highlight"><c- n>T1</c-></code> and <code class="highlight"><c- n>T2</c-></code> are <code class="highlight"><c- b>void</c-></code> or <code class="highlight"><c- o>*</c-><c- n>x</c-> <c- o>!=</c-> <c- o>*</c-><c- n>y</c-></code> and <code class="highlight"><c- n>x</c-><c- p>.</c-><c- n>error</c-><c- p>()</c-> <c- o>!=</c-> <c- n>y</c-><c- p>.</c-><c- n>error</c-><c- p>()</c-></code> are core
constant expression, shall be constexpr functions.</p>
   <h3 class="heading settled" data-level="1.12" id="expected.comparison_T"><span class="secno">1.12. </span><span class="content">�.�.4.7 Comparison with <code class="highlight"><c- n>T</c-></code> [<em>expected.comparison_T</em>]</span><a class="self-link" href="#expected.comparison_T"></a></h3>
<pre class="language-c++ highlight"><c- n>template</c-> <c- o>&lt;</c-><c- n>class</c-> <c- n>T1</c-><c- p>,</c-> <c- n>class</c-> <c- n>E1</c-><c- p>,</c-> <c- n>class</c-> <c- n>T2</c-><c- o>></c-> <c- n>constexpr</c-> <c- b>bool</c-> <c- n>operator</c-><c- o>==</c-><c- p>(</c-><c- k>const</c-> <c- n>expected</c-><c- o>&lt;</c-><c- n>T1</c-><c- p>,</c-> <c- n>E1</c-><c- o>>&amp;</c-> <c- n>x</c-><c- p>,</c-> <c- k>const</c-> <c- n>T2</c-><c- o>&amp;</c-> <c- n>v</c-><c- p>);</c->
<c- n>template</c-> <c- o>&lt;</c-><c- n>class</c-> <c- n>T1</c-><c- p>,</c-> <c- n>class</c-> <c- n>E1</c-><c- p>,</c-> <c- n>class</c-> <c- n>T2</c-><c- o>></c-> <c- n>constexpr</c-> <c- b>bool</c-> <c- n>operator</c-><c- o>==</c-><c- p>(</c-><c- k>const</c-> <c- n>T2</c-><c- o>&amp;</c-> <c- n>v</c-><c- p>,</c-> <c- k>const</c-> <c- n>expected</c-><c- o>&lt;</c-><c- n>T1</c-><c- p>,</c-> <c- n>E1</c-><c- o>>&amp;</c-> <c- n>x</c-><c- p>);</c->
</pre>
   <p><em>Requires</em>: <code class="highlight"><c- n>T1</c-></code> and <code class="highlight"><c- n>T2</c-></code> are not <code class="highlight"><c- b>void</c-></code> and the expression <code class="highlight"><c- o>*</c-><c- n>x</c-> <c- o>==</c-> <c- n>v</c-></code> shall be well-formed
and its result shall be convertible to <code class="highlight"><c- b>bool</c-></code>. [ <em>Note:</em> <code class="highlight"><c- n>T1</c-></code> need not be <em>EqualityComparable</em>. - <em>end note</em>]</p>
   <p><em>Returns</em>: <code class="highlight"><c- b>bool</c-><c- p>(</c-><c- n>x</c-><c- p>)</c-> <c- o>?</c-> <c- o>*</c-><c- n>x</c-> <c- o>==</c-> <c- nl>v</c-> <c- p>:</c-> false<c- p>;</c-></code>.</p>
<pre class="language-c++ highlight"><c- n>template</c-> <c- o>&lt;</c-><c- n>class</c-> <c- n>T1</c-><c- p>,</c-> <c- n>class</c-> <c- n>E1</c-><c- p>,</c-> <c- n>class</c-> <c- n>T2</c-><c- o>></c-> <c- n>constexpr</c-> <c- b>bool</c-> <c- n>operator</c-><c- o>!=</c-><c- p>(</c-><c- k>const</c-> <c- n>expected</c-><c- o>&lt;</c-><c- n>T1</c-><c- p>,</c-> <c- n>E1</c-><c- o>>&amp;</c-> <c- n>x</c-><c- p>,</c-> <c- k>const</c-> <c- n>T2</c-><c- o>&amp;</c-> <c- n>v</c-><c- p>);</c->
<c- n>template</c-> <c- o>&lt;</c-><c- n>class</c-> <c- n>T1</c-><c- p>,</c-> <c- n>class</c-> <c- n>E1</c-><c- p>,</c-> <c- n>class</c-> <c- n>T2</c-><c- o>></c-> <c- n>constexpr</c-> <c- b>bool</c-> <c- n>operator</c-><c- o>!=</c-><c- p>(</c-><c- k>const</c-> <c- n>T2</c-><c- o>&amp;</c-> <c- n>v</c-><c- p>,</c-> <c- k>const</c-> <c- n>expected</c-><c- o>&lt;</c-><c- n>T1</c-><c- p>,</c-> <c- n>E1</c-><c- o>>&amp;</c-> <c- n>x</c-><c- p>);</c->
</pre>
   <p><em>Requires</em>: <code class="highlight"><c- n>T1</c-></code> and <code class="highlight"><c- n>T2</c-></code> are not <code class="highlight"><c- b>void</c-></code> and the expression <code class="highlight"><c- o>*</c-><c- n>x</c-> <c- o>==</c-> <c- n>v</c-></code> shall be well-formed
and its result shall be convertible to <code class="highlight"><c- b>bool</c-></code>. [ <em>Note:</em> <code class="highlight"><c- n>T1</c-></code> need not be <em>EqualityComparable</em>. - <em>end note</em>]</p>
   <p><em>Returns</em>: <code class="highlight"><c- b>bool</c-><c- p>(</c-><c- n>x</c-><c- p>)</c-> <c- o>?</c-> <c- o>*</c-><c- n>x</c-> <c- o>!=</c-> <c- nl>v</c-> <c- p>:</c-> false<c- p>;</c-></code>.</p>
   <h3 class="heading settled" data-level="1.13" id="expected.comparison_unexpected_E"><span class="secno">1.13. </span><span class="content">�.�.4.8 Comparison with <code class="highlight"><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code> [<em>expected.comparison_unexpected_E</em>]</span><a class="self-link" href="#expected.comparison_unexpected_E"></a></h3>
<pre class="language-c++ highlight"><c- n>template</c-> <c- o>&lt;</c-><c- n>class</c-> <c- n>T1</c-><c- p>,</c-> <c- n>class</c-> <c- n>E1</c-><c- p>,</c-> <c- n>class</c-> <c- n>E2</c-><c- o>></c-> <c- n>constexpr</c-> <c- b>bool</c-> <c- n>operator</c-><c- o>==</c-><c- p>(</c-><c- k>const</c-> <c- n>expected</c-><c- o>&lt;</c-><c- n>T1</c-><c- p>,</c-> <c- n>E1</c-><c- o>>&amp;</c-> <c- n>x</c-><c- p>,</c-> <c- k>const</c-> <c- n>unexpected</c-><c- o>&lt;</c-><c- n>E2</c-><c- o>>&amp;</c-> <c- n>e</c-><c- p>);</c->
<c- n>template</c-> <c- o>&lt;</c-><c- n>class</c-> <c- n>T1</c-><c- p>,</c-> <c- n>class</c-> <c- n>E1</c-><c- p>,</c-> <c- n>class</c-> <c- n>E2</c-><c- o>></c-> <c- n>constexpr</c-> <c- b>bool</c-> <c- n>operator</c-><c- o>==</c-><c- p>(</c-><c- k>const</c-> <c- n>unexpected</c-><c- o>&lt;</c-><c- n>E2</c-><c- o>>&amp;</c-> <c- n>e</c-><c- p>,</c-> <c- k>const</c-> <c- n>expected</c-><c- o>&lt;</c-><c- n>T1</c-><c- p>,</c-> <c- n>E1</c-><c- o>>&amp;</c-> <c- n>x</c-><c- p>);</c->
</pre>
   <p><em>Requires</em>: The expression <code class="highlight"><c- n>unexpected</c-><c- p>(</c-><c- n>x</c-><c- p>.</c-><c- n>error</c-><c- p>())</c-> <c- o>==</c-> <c- n>e</c-></code> shall be well-formed and
its result shall be convertible to <code class="highlight"><c- b>bool</c-></code>.</p>
   <p><em>Returns</em>: <code class="highlight"><c- b>bool</c-><c- p>(</c-><c- n>x</c-><c- p>)</c-> <c- o>?</c-> false <c- o>:</c-> <c- n>unexpected</c-><c- p>(</c-><c- n>x</c-><c- p>.</c-><c- n>error</c-><c- p>())</c-> <c- o>==</c-> <c- n>e</c-><c- p>;</c-></code>.</p>
<pre class="language-c++ highlight"><c- n>template</c-> <c- o>&lt;</c-><c- n>class</c-> <c- n>T1</c-><c- p>,</c-> <c- n>class</c-> <c- n>E1</c-><c- p>,</c-> <c- n>class</c-> <c- n>E2</c-><c- o>></c-> <c- n>constexpr</c-> <c- b>bool</c-> <c- n>operator</c-><c- o>!=</c-><c- p>(</c-><c- k>const</c-> <c- n>expected</c-><c- o>&lt;</c-><c- n>T1</c-><c- p>,</c-> <c- n>E1</c-><c- o>>&amp;</c-> <c- n>x</c-><c- p>,</c-> <c- k>const</c-> <c- n>unexpected</c-><c- o>&lt;</c-><c- n>E2</c-><c- o>>&amp;</c-> <c- n>e</c-><c- p>);</c->
<c- n>template</c-> <c- o>&lt;</c-><c- n>class</c-> <c- n>T1</c-><c- p>,</c-> <c- n>class</c-> <c- n>E1</c-><c- p>,</c-> <c- n>class</c-> <c- n>E2</c-><c- o>></c-> <c- n>constexpr</c-> <c- b>bool</c-> <c- n>operator</c-><c- o>!=</c-><c- p>(</c-><c- k>const</c-> <c- n>unexpected</c-><c- o>&lt;</c-><c- n>E2</c-><c- o>>&amp;</c-> <c- n>e</c-><c- p>,</c-> <c- k>const</c-> <c- n>expected</c-><c- o>&lt;</c-><c- n>T1</c-><c- p>,</c-> <c- n>E1</c-><c- o>>&amp;</c-> <c- n>x</c-><c- p>);</c->
</pre>
   <p><em>Requires</em>: The expression <code class="highlight"><c- n>unexpected</c-><c- p>(</c-><c- n>x</c-><c- p>.</c-><c- n>error</c-><c- p>())</c-> <c- o>!=</c-> <c- n>e</c-></code> shall be well-formed and
its result shall be convertible to <code class="highlight"><c- b>bool</c-></code>. <em>Returns</em>: <code class="highlight"><c- b>bool</c-><c- p>(</c-><c- n>x</c-><c- p>)</c-> <c- o>?</c-> true <c- o>:</c-> <c- n>unexpected</c-><c- p>(</c-><c- n>x</c-><c- p>.</c-><c- n>error</c-><c- p>())</c-> <c- o>!=</c-> <c- n>e</c-><c- p>;</c-></code>.</p>
   <h3 class="heading settled" data-level="1.14" id="expected.specalg"><span class="secno">1.14. </span><span class="content">�.�.4.9 Specialized algorithms [<em>expected.specalg</em>]</span><a class="self-link" href="#expected.specalg"></a></h3>
<pre class="language-c++ highlight"><c- n>template</c-> <c- o>&lt;</c-><c- n>class</c-> <c- n>T1</c-><c- p>,</c-> <c- n>class</c-> <c- n>E1</c-><c- o>></c->
<c- b>void</c-> <c- n>swap</c-><c- p>(</c-><c- n>expected</c-><c- o>&lt;</c-><c- n>T1</c-><c- p>,</c-> <c- n>E1</c-><c- o>>&amp;</c-> <c- n>x</c-><c- p>,</c-> <c- n>expected</c-><c- o>&lt;</c-><c- n>T1</c-><c- p>,</c-> <c- n>E1</c-><c- o>>&amp;</c-> <c- n>y</c-><c- p>)</c-> <c- n>noexcept</c-><c- p>(</c-><c- n>noexcept</c-><c- p>(</c-><c- n>x</c-><c- p>.</c-><c- n>swap</c-><c- p>(</c-><c- n>y</c-><c- p>)));</c->
</pre>
   <p><em>Effects</em>: Calls <code class="highlight"><c- n>x</c-><c- p>.</c-><c- n>swap</c-><c- p>(</c-><c- n>y</c-><c- p>)</c-></code>.</p>
   <p><em>Remarks</em>: This function shall not participate in overload resolution unless <code class="highlight"><c- n>T1</c-></code> is <code class="highlight"><c- b>void</c-></code> or <code class="highlight"><c- n>is_move_constructible_v</c-><c- o>&lt;</c-><c- n>T1</c-><c- o>></c-></code> is <code class="highlight">true</code>, <code class="highlight"><c- n>is_swappable_v</c-><c- o>&lt;</c-><c- n>T1</c-><c- o>></c-></code> is <code class="highlight">true</code> and <code class="highlight"><c- n>is_move_constructible_v</c-><c- o>&lt;</c-><c- n>E1</c-><c- o>></c-></code> is <code class="highlight">true</code> and <code class="highlight"><c- n>is_swappable_v</c-><c- o>&lt;</c-><c- n>E1</c-><c- o>></c-></code> is <code class="highlight">true</code>.</p>
   <h3 class="heading settled" data-level="1.15" id="expected.unexpected"><span class="secno">1.15. </span><span class="content">�.�.5 Unexpected objects [<em>expected.unexpected</em>]</span><a class="self-link" href="#expected.unexpected"></a></h3>
   <h3 class="heading settled" data-level="1.16" id="expected.unexpected.general"><span class="secno">1.16. </span><span class="content">�.�.5.1 General [<em>expected.unexpected.general</em>]</span><a class="self-link" href="#expected.unexpected.general"></a></h3>
   <p>This subclause describes class template <code class="highlight"><c- n>unexpected</c-></code> that
represents unexpected objects.</p>
   <h3 class="heading settled" data-level="1.17" id="expected.unexpected.object"><span class="secno">1.17. </span><span class="content">�.�.5.2 Class template <code class="highlight"><c- n>unexpected</c-></code> [<em>expected.unexpected.object</em>]</span><a class="self-link" href="#expected.unexpected.object"></a></h3>
<pre class="language-c++ highlight"><c- n>template</c-> <c- o>&lt;</c-><c- n>class</c-> <c- n>E</c-><c- o>></c->
<c- n>class</c-> <c- n>unexpected</c-> <c- p>{</c->
<c- nl>public</c-><c- p>:</c->
    <c- n>constexpr</c-> <c- n>unexpected</c-><c- p>(</c-><c- k>const</c-> <c- n>unexpected</c-><c- o>&amp;</c-><c- p>)</c-> <c- o>=</c-> <c- k>default</c-><c- p>;</c->
    <c- n>constexpr</c-> <c- nf>unexpected</c-><c- p>(</c-><c- n>unexpected</c-><c- o>&amp;&amp;</c-><c- p>)</c-> <c- o>=</c-> <c- k>default</c-><c- p>;</c->
	<c- n>template</c-> <c- o>&lt;</c-><c- n>class</c-><c- p>...</c-> <c- n>Args</c-><c- o>></c->
		<c- n>constexpr</c-> <c- n>explicit</c-> <c- n>unexpected</c-><c- p>(</c-><c- n>in_place_t</c-><c- p>,</c-> <c- n>Args</c-><c- o>&amp;&amp;</c-><c- p>...);</c->
    <c- n>template</c-> <c- o>&lt;</c-><c- n>class</c-> <c- n>U</c-><c- p>,</c-> <c- n>class</c-><c- p>...</c-> <c- n>Args</c-><c- o>></c->
		<c- n>constexpr</c-> <c- n>explicit</c-> <c- n>unexpected</c-><c- p>(</c-><c- n>in_place_t</c-><c- p>,</c-> <c- n>initializer_list</c-><c- o>&lt;</c-><c- n>U</c-><c- o>></c-><c- p>,</c-> <c- n>Args</c-><c- o>&amp;&amp;</c-><c- p>...);</c->
    <c- n>template</c-> <c- o>&lt;</c-><c- n>class</c-> <c- n>Err</c-> <c- o>=</c-> <c- n>E</c-><c- o>></c->
		<c- n>constexpr</c-> <c- n>explicit</c-> <c- n>unexpected</c-><c- p>(</c-><c- n>Err</c-><c- o>&amp;&amp;</c-><c- p>);</c->
    <c- n>template</c-> <c- o>&lt;</c-><c- n>class</c-> <c- n>Err</c-><c- o>></c->
		<c- n>constexpr</c-> <c- n>EXPLICIT</c-> <c- n>unexpected</c-><c- p>(</c-><c- k>const</c-> <c- n>unexpected</c-><c- o>&lt;</c-><c- n>Err</c-><c- o>>&amp;</c-><c- p>);</c->
    <c- n>template</c-> <c- o>&lt;</c-><c- n>class</c-> <c- n>Err</c-><c- o>></c->
		<c- n>constexpr</c-> <c- n>EXPLICIT</c-> <c- n>unexpected</c-><c- p>(</c-><c- n>unexpected</c-><c- o>&lt;</c-><c- n>Err</c-><c- o>>&amp;&amp;</c-><c- p>);</c->

    <c- n>constexpr</c-> <c- n>unexpected</c-><c- o>&amp;</c-> <c- n>operator</c-><c- o>=</c-><c- p>(</c-><c- k>const</c-> <c- n>unexpected</c-><c- o>&amp;</c-><c- p>)</c-> <c- o>=</c-> <c- k>default</c-><c- p>;</c->
    <c- n>constexpr</c-> <c- n>unexpected</c-><c- o>&amp;</c-> <c- n>operator</c-><c- o>=</c-><c- p>(</c-><c- n>unexpected</c-><c- o>&amp;&amp;</c-><c- p>)</c-> <c- o>=</c-> <c- k>default</c-><c- p>;</c->
	<c- n>template</c-> <c- o>&lt;</c-><c- n>class</c-> <c- n>Err</c-> <c- o>=</c-> <c- n>E</c-><c- o>></c->
    <c- n>constexpr</c-> <c- n>unexpected</c-><c- o>&amp;</c-> <c- n>operator</c-><c- o>=</c-><c- p>(</c-><c- k>const</c-> <c- n>unexpected</c-><c- o>&lt;</c-><c- n>Err</c-><c- o>>&amp;</c-><c- p>);</c->
	<c- n>template</c-> <c- o>&lt;</c-><c- n>class</c-> <c- n>Err</c-> <c- o>=</c-> <c- n>E</c-><c- o>></c->
    <c- n>constexpr</c-> <c- n>unexpected</c-><c- o>&amp;</c-> <c- n>operator</c-><c- o>=</c-><c- p>(</c-><c- n>unexpected</c-><c- o>&lt;</c-><c- n>Err</c-><c- o>>&amp;&amp;</c-><c- p>);</c->
	
    <c- n>constexpr</c-> <c- k>const</c-> <c- n>E</c-><c- o>&amp;</c-> <c- n>value</c-><c- p>()</c-> <c- k>const</c-><c- o>&amp;</c-> <c- n>noexcept</c-><c- p>;</c->
    <c- n>constexpr</c-> <c- n>E</c-><c- o>&amp;</c-> <c- n>value</c-><c- p>()</c-> <c- o>&amp;</c-> <c- n>noexcept</c-><c- p>;</c->
    <c- n>constexpr</c-> <c- k>const</c-> <c- n>E</c-><c- o>&amp;&amp;</c-> <c- n>value</c-><c- p>()</c-> <c- k>const</c-><c- o>&amp;&amp;</c-> <c- n>noexcept</c-><c- p>;</c->
    <c- n>constexpr</c-> <c- n>E</c-><c- o>&amp;&amp;</c-> <c- n>value</c-><c- p>()</c-> <c- o>&amp;&amp;</c-> <c- n>noexcept</c-><c- p>;</c->

	<c- b>void</c-> <c- nf>swap</c-><c- p>(</c-><c- n>unexpected</c-><c- o>&amp;</c-> <c- n>other</c-><c- p>)</c-> <c- n>noexcept</c-><c- p>(</c-><c- n>see</c-> <c- n>bellow</c-><c- p>);</c->
	
    <c- n>template</c-> <c- o>&lt;</c-><c- n>class</c-> <c- n>E1</c-><c- p>,</c-> <c- n>class</c-> <c- n>E2</c-><c- o>></c->
        <c- n>friend</c-> <c- n>constexpr</c-> <c- b>bool</c->
        <c- n>operator</c-><c- o>==</c-><c- p>(</c-><c- k>const</c-> <c- n>unexpected</c-><c- o>&lt;</c-><c- n>E1</c-><c- o>>&amp;</c-><c- p>,</c-> <c- k>const</c-> <c- n>unexpected</c-><c- o>&lt;</c-><c- n>E2</c-><c- o>>&amp;</c-><c- p>);</c->
    <c- n>template</c-> <c- o>&lt;</c-><c- n>class</c-> <c- n>E1</c-><c- p>,</c-> <c- n>class</c-> <c- n>E2</c-><c- o>></c->
        <c- n>constexpr</c-> <c- b>bool</c->
        <c- n>operator</c-><c- o>!=</c-><c- p>(</c-><c- k>const</c-> <c- n>unexpected</c-><c- o>&lt;</c-><c- n>E1</c-><c- o>>&amp;</c-><c- p>,</c-> <c- k>const</c-> <c- n>unexpected</c-><c- o>&lt;</c-><c- n>E2</c-><c- o>>&amp;</c-><c- p>);</c->

    <c- n>template</c-> <c- o>&lt;</c-><c- n>class</c-> <c- n>E1</c-><c- o>></c->
    <c- n>friend</c-> <c- b>void</c-> <c- n>swap</c-><c- p>(</c-><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E1</c-><c- o>>&amp;</c-> <c- n>x</c-><c- p>,</c-> <c- n>unexpected</c-><c- o>&lt;</c-><c- n>E1</c-><c- o>>&amp;</c-> <c- n>y</c-><c- p>)</c-> <c- n>noexcept</c-><c- p>(</c-><c- n>noexcept</c-><c- p>(</c-><c- n>x</c-><c- p>.</c-><c- n>swap</c-><c- p>(</c-><c- n>y</c-><c- p>)));</c->
	

<c- nl>private</c-><c- p>:</c->
    <c- n>E</c-> <c- n>val</c-><c- p>;</c-> <c- c1>// exposition only</c->
<c- p>};</c->

<c- n>template</c-> <c- o>&lt;</c-><c- n>class</c-> <c- n>E</c-><c- o>></c-> <c- n>unexpected</c-><c- p>(</c-><c- n>E</c-><c- p>)</c-> <c- o>-></c-> <c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-><c- p>;</c->
</pre>
   <p>�.�.5.2.1 Constructors [<em>expected.unexpected.ctor</em>] {#expected.unexpected.ctor}</p>
<pre class="language-c++ highlight"><c- n>template</c-> <c- o>&lt;</c-><c- n>class</c-> <c- n>Err</c-><c- o>></c->
	<c- n>constexpr</c-> <c- n>explicit</c-> <c- n>unexpected</c-><c- p>(</c-><c- n>Err</c-><c- o>&amp;&amp;</c-> <c- n>e</c-><c- p>);</c->
</pre>
   <p><em>Effects</em>: Initializes <code class="highlight"><c- n>val</c-></code> as if direct-non-list-initializing an
object of type <code class="highlight"><c- n>E</c-></code> with the expression <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>forward</c-><c- o>&lt;</c-><c- n>Err</c-><c- o>></c-><c- p>(</c-><c- n>e</c-><c- p>)</c-></code>.</p>
   <p><em>Throws</em>: Any exception thrown by the selected constructor of <code class="highlight"><c- n>E</c-></code>.</p>
   <p><em>Remarks</em>:
If E’s selected constructor is a constexpr constructor, this constructor shall be a constexpr constructor.
This constructor shall not participate in overload resolution unless <code class="highlight"><c- n>is_constructible_v</c-><c- o>&lt;</c-><c- n>E</c-><c- p>,</c-> <c- n>Err</c-><c- o>&amp;&amp;></c-></code> is <code class="highlight">true</code>, <code class="highlight"><c- n>is_same_v</c-><c- o>&lt;</c-><c- n>remove_cvref_t</c-><c- o>&lt;</c-><c- n>U</c-><c- o>></c-><c- p>,</c-> <c- n>in_place_t</c-><c- o>></c-></code> is <code class="highlight">false</code> and <code class="highlight"><c- n>is_same_v</c-><c- o>&lt;</c-><c- n>remove_cvref_t</c-><c- o>&lt;</c-><c- n>U</c-><c- o>></c-><c- p>,</c-> <c- n>unexpected</c-><c- o>></c-></code> is <code class="highlight">false</code>.</p>
<pre class="language-c++ highlight"><c- n>template</c-> <c- o>&lt;</c-><c- n>class</c-><c- p>...</c-> <c- n>Args</c-><c- o>></c->
	<c- n>constexpr</c-> <c- n>explicit</c-> <c- n>unexpected</c-><c- p>(</c-><c- n>in_place_t</c-><c- p>,</c-> <c- n>Args</c-><c- o>&amp;&amp;</c-><c- p>...);</c->
</pre>
   <p><em>Effects</em>: Initializes <code class="highlight"><c- n>val</c-></code> as if direct-non-list-initializing an
object of type <code class="highlight"><c- n>E</c-></code> with the arguments <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>forward</c-><c- o>&lt;</c-><c- n>Args</c-><c- o>></c-><c- p>(</c-><c- n>args</c-><c- p>)...</c-></code>.</p>
   <p><em>Throws</em>: Any exception thrown by the selected constructor of <code class="highlight"><c- n>E</c-></code>.</p>
   <p><em>Remarks</em>:
If E’s selected constructor is a constexpr constructor, this constructor shall be a constexpr constructor.
This constructor shall not participate in overload resolution unless <code class="highlight"><c- n>is_constructible_v</c-><c- o>&lt;</c-><c- n>E</c-><c- p>,</c-> <c- n>Args</c-><c- o>&amp;&amp;</c-><c- p>...</c-><c- o>></c-></code> is <code class="highlight">true</code>.</p>
<pre class="language-c++ highlight"><c- n>template</c-> <c- o>&lt;</c-><c- n>class</c-> <c- n>U</c-><c- p>,</c-> <c- n>class</c-><c- p>...</c-> <c- n>Args</c-><c- o>></c->
	<c- n>constexpr</c-> <c- n>explicit</c-> <c- n>unexpected</c-><c- p>(</c-><c- n>in_place_t</c-><c- p>,</c-> <c- n>initializer_list</c-><c- o>&lt;</c-><c- n>U</c-><c- o>></c-><c- p>,</c-> <c- n>Args</c-><c- o>&amp;&amp;</c-><c- p>...);</c->
</pre>
   <p><em>Effects</em>: Initializes <code class="highlight"><c- n>val</c-></code> as if direct-non-list-initializing an
object of type <code class="highlight"><c- n>E</c-></code> with the arguments <code class="highlight"><c- n>il</c-><c- p>,</c-> <c- n>std</c-><c- o>::</c-><c- n>forward</c-><c- o>&lt;</c-><c- n>Args</c-><c- o>></c-><c- p>(</c-><c- n>args</c-><c- p>)...</c-></code>.</p>
   <p><em>Throws</em>: Any exception thrown by the selected constructor of <code class="highlight"><c- n>E</c-></code>.</p>
   <p><em>Remarks</em>:
If E’s selected constructor is a constexpr constructor, this constructor shall be a constexpr constructor.
This constructor shall not participate in overload resolution unless <code class="highlight"><c- n>is_constructible_v</c-><c- o>&lt;</c-><c- n>E</c-><c- p>,</c-> <c- n>initializer_list</c-><c- o>&lt;</c-><c- n>U</c-><c- o>>&amp;</c-><c- p>,</c-> <c- n>Args</c-><c- o>&amp;&amp;</c-><c- p>...</c-><c- o>></c-></code> is <code class="highlight">true</code>.</p>
<pre class="language-c++ highlight"><c- n>template</c-> <c- o>&lt;</c-><c- n>class</c-> <c- n>Err</c-><c- o>></c->
<c- n>constexpr</c-> <c- n>EXPLICIT</c-> <c- n>unexpected</c-><c- p>(</c-><c- k>const</c-> <c- n>unexpected</c-><c- o>&lt;</c-><c- n>Err</c-><c- o>>&amp;</c-> <c- n>e</c-><c- p>);</c->
</pre>
   <p><em>Effects</em>: Initializes <code class="highlight"><c- n>val</c-></code> as if direct-non-list-initializing an
object of type <code class="highlight"><c- n>E</c-></code> with the expression <code class="highlight"><c- n>e</c-><c- p>.</c-><c- n>val</c-></code>.</p>
   <p><em>Throws</em>: Any exception thrown by the selected constructor of <code class="highlight"><c- n>E</c-></code>.</p>
   <p><em>Remarks</em>: This constructor participates in overload resolution unless</p>
   <ul>
    <li data-md>
     <p><code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>is_constructible_v</c-><c- o>&lt;</c-><c- n>E</c-><c- p>,</c-> <c- n>Err</c-><c- o>></c-></code> is <code class="highlight">true</code>,</p>
    <li data-md>
     <p><code class="highlight"><c- n>is_constructible_v</c-><c- o>&lt;</c-><c- n>E</c-><c- p>,</c-> <c- n>unexpected</c-><c- o>&lt;</c-><c- n>Err</c-><c- o>>&amp;></c-></code> is <code class="highlight">false</code>,</p>
    <li data-md>
     <p><code class="highlight"><c- n>is_constructible_v</c-><c- o>&lt;</c-><c- n>E</c-><c- p>,</c-> <c- n>unexpected</c-><c- o>&lt;</c-><c- n>Err</c-><c- o>>&amp;&amp;></c-></code> is <code class="highlight">false</code>,</p>
    <li data-md>
     <p><code class="highlight"><c- n>is_constructible_v</c-><c- o>&lt;</c-><c- n>E</c-><c- p>,</c-> <c- k>const</c-> <c- n>unexpected</c-><c- o>&lt;</c-><c- n>Err</c-><c- o>>&amp;></c-></code> is <code class="highlight">false</code>,</p>
    <li data-md>
     <p><code class="highlight"><c- n>is_constructible_v</c-><c- o>&lt;</c-><c- n>E</c-><c- p>,</c-> <c- k>const</c-> <c- n>unexpected</c-><c- o>&lt;</c-><c- n>Err</c-><c- o>>&amp;&amp;></c-></code> is <code class="highlight">false</code>,</p>
    <li data-md>
     <p><code class="highlight"><c- n>is_convertible_v</c-><c- o>&lt;</c-><c- n>unexpected</c-><c- o>&lt;</c-><c- n>Err</c-><c- o>>&amp;</c-><c- p>,</c-> <c- n>E</c-><c- o>></c-></code> is <code class="highlight">false</code>,</p>
    <li data-md>
     <p><code class="highlight"><c- n>is_convertible_v</c-><c- o>&lt;</c-><c- n>unexpected</c-><c- o>&lt;</c-><c- n>Err</c-><c- o>>&amp;&amp;</c-><c- p>,</c-> <c- n>E</c-><c- o>></c-></code> is <code class="highlight">false</code>,</p>
    <li data-md>
     <p><code class="highlight"><c- n>is_convertible_v</c-><c- o>&lt;</c-><c- k>const</c-> <c- n>unexpected</c-><c- o>&lt;</c-><c- n>Err</c-><c- o>>&amp;</c-><c- p>,</c-> <c- n>E</c-><c- o>></c-></code> is <code class="highlight">false</code>, and</p>
    <li data-md>
     <p><code class="highlight"><c- n>is_convertible_v</c-><c- o>&lt;</c-><c- k>const</c-> <c- n>unexpected</c-><c- o>&lt;</c-><c- n>Err</c-><c- o>>&amp;&amp;</c-><c- p>,</c-> <c- n>E</c-><c- o>></c-></code> is <code class="highlight">false</code>.</p>
   </ul>
   <p>This constructor is <code class="highlight"><c- k>explicit</c-></code> if and only if <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>is_convertible_v</c-><c- o>&lt;</c-><c- n>Err</c-><c- p>,</c-> <c- n>E</c-><c- o>></c-></code> is <code class="highlight">false</code>.</p>
<pre class="language-c++ highlight"><c- n>template</c-> <c- o>&lt;</c-><c- n>class</c-> <c- n>Err</c-><c- o>></c->
<c- n>constexpr</c-> <c- n>EXPLICIT</c-> <c- n>unexpected</c-><c- p>(</c-><c- n>unexpected</c-><c- o>&lt;</c-><c- n>Err</c-><c- o>></c-> <c- o>&amp;&amp;</c-> <c- n>e</c-><c- p>);</c->
</pre>
   <p><em>Effects</em>: Initializes <code class="highlight"><c- n>val</c-></code> as if direct-non-list-initializing an
object of type <code class="highlight"><c- n>E</c-></code> with the expression <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>move</c-><c- p>(</c-><c- n>e</c-><c- p>.</c-><c- n>val</c-><c- p>)</c-></code>.</p>
   <p><em>Throws</em>: Any exception thrown by the selected constructor of <code class="highlight"><c- n>E</c-></code>.</p>
   <p><em>Remarks</em>: This constructor participates in overload resolution unless</p>
   <ul>
    <li data-md>
     <p><code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>is_constructible_v</c-><c- o>&lt;</c-><c- n>E</c-><c- p>,</c-> <c- n>Err</c-><c- o>&amp;&amp;></c-></code> is <code class="highlight">true</code>,</p>
    <li data-md>
     <p><code class="highlight"><c- n>is_constructible_v</c-><c- o>&lt;</c-><c- n>E</c-><c- p>,</c-> <c- n>unexpected</c-><c- o>&lt;</c-><c- n>Err</c-><c- o>>&amp;></c-></code> is <code class="highlight">false</code>,</p>
    <li data-md>
     <p><code class="highlight"><c- n>is_constructible_v</c-><c- o>&lt;</c-><c- n>E</c-><c- p>,</c-> <c- n>unexpected</c-><c- o>&lt;</c-><c- n>Err</c-><c- o>>&amp;&amp;></c-></code> is <code class="highlight">false</code>,</p>
    <li data-md>
     <p><code class="highlight"><c- n>is_constructible_v</c-><c- o>&lt;</c-><c- n>E</c-><c- p>,</c-> <c- k>const</c-> <c- n>unexpected</c-><c- o>&lt;</c-><c- n>Err</c-><c- o>>&amp;></c-></code> is <code class="highlight">false</code>,</p>
    <li data-md>
     <p><code class="highlight"><c- n>is_constructible_v</c-><c- o>&lt;</c-><c- n>E</c-><c- p>,</c-> <c- k>const</c-> <c- n>unexpected</c-><c- o>&lt;</c-><c- n>Err</c-><c- o>>&amp;&amp;></c-></code> is <code class="highlight">false</code>,</p>
    <li data-md>
     <p><code class="highlight"><c- n>is_convertible_v</c-><c- o>&lt;</c-><c- n>unexpected</c-><c- o>&lt;</c-><c- n>Err</c-><c- o>>&amp;</c-><c- p>,</c-> <c- n>E</c-><c- o>></c-></code> is <code class="highlight">false</code>,</p>
    <li data-md>
     <p><code class="highlight"><c- n>is_convertible_v</c-><c- o>&lt;</c-><c- n>unexpected</c-><c- o>&lt;</c-><c- n>Err</c-><c- o>>&amp;&amp;</c-><c- p>,</c-> <c- n>E</c-><c- o>></c-></code> is <code class="highlight">false</code>,</p>
    <li data-md>
     <p><code class="highlight"><c- n>is_convertible_v</c-><c- o>&lt;</c-><c- k>const</c-> <c- n>unexpected</c-><c- o>&lt;</c-><c- n>Err</c-><c- o>>&amp;</c-><c- p>,</c-> <c- n>E</c-><c- o>></c-></code> is <code class="highlight">false</code>, and</p>
    <li data-md>
     <p><code class="highlight"><c- n>is_convertible_v</c-><c- o>&lt;</c-><c- k>const</c-> <c- n>unexpected</c-><c- o>&lt;</c-><c- n>Err</c-><c- o>>&amp;&amp;</c-><c- p>,</c-> <c- n>E</c-><c- o>></c-></code> is <code class="highlight">false</code>.</p>
   </ul>
   <p>This constructor is <code class="highlight"><c- k>explicit</c-></code> if and only if <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>is_convertible_v</c-><c- o>&lt;</c-><c- n>Err</c-><c- o>&amp;&amp;</c-><c- p>,</c-> <c- n>E</c-><c- o>></c-></code> is <code class="highlight">false</code></p>
   <p>�.�.5.2.2 Assignment [<em>expected.unexpected.assign</em>] {#expected.unexpected.assign}</p>
   <p>�.�.5.2.3 Observers [<em>expected.unexpected.observe</em>] {#expected.unexpected.observe}</p>
<pre class="language-c++ highlight"><c- n>constexpr</c-> <c- k>const</c-> <c- n>E</c-><c- o>&amp;</c-> <c- n>value</c-><c- p>()</c-> <c- k>const</c-> <c- o>&amp;</c-><c- p>;</c->
<c- n>constexpr</c-> <c- n>E</c-><c- o>&amp;</c-> <c- n>value</c-><c- p>()</c-> <c- o>&amp;</c-><c- p>;</c->
</pre>
   <p><em>Returns</em>: <code class="highlight"><c- n>val</c-></code>.</p>
<pre class="language-c++ highlight"><c- n>constexpr</c-> <c- n>E</c-><c- o>&amp;&amp;</c-> <c- n>value</c-><c- p>()</c-> <c- o>&amp;&amp;</c-><c- p>;</c->
<c- n>constexpr</c-> <c- n>E</c-> <c- k>const</c-><c- o>&amp;&amp;</c-> <c- n>value</c-><c- p>()</c-> <c- k>const</c-><c- o>&amp;&amp;</c-><c- p>;</c->
</pre>
   <p><em>Returns</em>: <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>move</c-><c- p>(</c-><c- n>val</c-><c- p>)</c-></code>.</p>
   <p>�.�.5.2.4 Swap [<em>expected.unexpected.ctor</em>] {#expected.unexpected.swap}</p>
<pre class="language-c++ highlight">	<c- b>void</c-> <c- nf>swap</c-><c- p>(</c-><c- n>unexpected</c-><c- o>&amp;</c-> <c- n>other</c-><c- p>)</c-> <c- n>noexcept</c-><c- p>(</c-><c- n>see</c-> <c- n>bellow</c-><c- p>);</c->
</pre>
   <p><em>Requires</em>: <code class="highlight"><c- n>is_swappable_v</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code> is <code class="highlight">true</code></p>
   <p><em>Effects</em>: Equivalent to <code class="highlight"><c- k>using</c-> <c- n>std</c-><c- o>::</c-><c- n>swap</c-><c- p>;</c-> <c- n>swap</c-><c- p>(</c-><c- n>val</c-><c- p>,</c-> <c- n>other</c-><c- p>.</c-><c- n>val</c-><c- p>);</c-></code>.</p>
   <p><em>Throws</em>:</p>
   <p><em>Remarks</em>: The expression inside <code class="highlight"><c- k>noexcept</c-></code> is equivalent to: <code class="highlight"><c- n>is_nothrow_swappable_v</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code> is <code class="highlight">true</code>.</p>
   <h3 class="heading settled" data-level="1.18" id="expected.unexpected.equality_op"><span class="secno">1.18. </span><span class="content">�.�.5.2.5 Equality operators [<em>expected.unexpected.equality_op</em>]</span><a class="self-link" href="#expected.unexpected.equality_op"></a></h3>
<pre class="language-c++ highlight"><c- n>template</c-> <c- o>&lt;</c-><c- n>class</c-> <c- n>E1</c-><c- p>,</c-> <c- n>class</c-> <c- n>E2</c-><c- o>></c->
    <c- n>friend</c-> <c- n>constexpr</c-> <c- b>bool</c-> <c- n>operator</c-><c- o>==</c-><c- p>(</c-><c- k>const</c-> <c- n>unexpected</c-><c- o>&lt;</c-><c- n>E1</c-><c- o>>&amp;</c-> <c- n>x</c-><c- p>,</c-> <c- k>const</c-> <c- n>unexpected</c-><c- o>&lt;</c-><c- n>E2</c-><c- o>>&amp;</c-> <c- n>y</c-><c- p>);</c->
</pre>
   <p><em>Returns</em>: <code class="highlight"><c- n>x</c-><c- p>.</c-><c- n>value</c-><c- p>()</c-> <c- o>==</c-> <c- n>y</c-><c- p>.</c-><c- n>value</c-><c- p>()</c-></code>.</p>
<pre class="language-c++ highlight"><c- n>template</c-> <c- o>&lt;</c-><c- n>class</c-> <c- n>E1</c-><c- p>,</c-> <c- n>class</c-> <c- n>E2</c-><c- o>></c->
    <c- n>friend</c-> <c- n>constexpr</c-> <c- b>bool</c-> <c- n>operator</c-><c- o>!=</c-><c- p>(</c-><c- k>const</c-> <c- n>unexpected</c-><c- o>&lt;</c-><c- n>E1</c-><c- o>>&amp;</c-> <c- n>x</c-><c- p>,</c-> <c- k>const</c-> <c- n>unexpected</c-><c- o>&lt;</c-><c- n>E2</c-><c- o>>&amp;</c-> <c- n>y</c-><c- p>);</c->
</pre>
   <p><em>Returns</em>: <code class="highlight"><c- n>x</c-><c- p>.</c-><c- n>value</c-><c- p>()</c-> <c- o>!=</c-> <c- n>y</c-><c- p>.</c-><c- n>value</c-><c- p>()</c-></code>.</p>
   <p>�.�.5.2.5 Specialized algorithms [<em>expected.unexpected.specalg</em>] {#expected.unexpected.specalg}</p>
<pre class="language-c++ highlight"><c- n>template</c-> <c- o>&lt;</c-><c- n>class</c-> <c- n>E1</c-><c- o>></c->
    <c- n>friend</c-> <c- b>void</c-> <c- n>swap</c-><c- p>(</c-><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E1</c-><c- o>>&amp;</c-> <c- n>x</c-><c- p>,</c-> <c- n>unexpected</c-><c- o>&lt;</c-><c- n>E1</c-><c- o>>&amp;</c-> <c- n>y</c-><c- p>)</c-> <c- n>noexcept</c-><c- p>(</c-><c- n>noexcept</c-><c- p>(</c-><c- n>x</c-><c- p>.</c-><c- n>swap</c-><c- p>(</c-><c- n>y</c-><c- p>)));</c->
</pre>
   <p><em>Effects</em>: Equivalent to <code class="highlight"><c- n>x</c-><c- p>.</c-><c- n>swap</c-><c- p>(</c-><c- n>y</c-><c- p>)</c-></code>.</p>
   <p><em>Remarks</em>: This function shall not participate in overload resolution unless <code class="highlight"><c- n>is_swappable_v</c-><c- o>&lt;</c-><c- n>E1</c-><c- o>></c-></code> is <code class="highlight">true</code>.</p>
   <h3 class="heading settled" data-level="1.19" id="expected.bad_expected_access"><span class="secno">1.19. </span><span class="content">�.�.6 Template Class <code class="highlight"><c- n>bad_expected_access</c-></code> [<em>expected.bad_expected_access</em>]</span><a class="self-link" href="#expected.bad_expected_access"></a></h3>
<pre class="language-c++ highlight"><c- n>template</c-> <c- o>&lt;</c-><c- n>class</c-> <c- n>E</c-><c- o>></c->
<c- n>class</c-> <c- nl>bad_expected_access</c-> <c- p>:</c-> <c- n>public</c-> <c- n>bad_expected_access</c-><c- o>&lt;</c-><c- b>void</c-><c- o>></c-> <c- p>{</c->
<c- nl>public</c-><c- p>:</c->
    <c- n>explicit</c-> <c- n>bad_expected_access</c-><c- p>(</c-><c- n>E</c-><c- p>);</c->
    <c- n>virtual</c-> <c- k>const</c-> <c- b>char</c-><c- o>*</c-> <c- nf>what</c-><c- p>()</c-> <c- k>const</c-> <c- n>noexcept</c-> <c- n>override</c-><c- p>;</c->
    <c- n>E</c-><c- o>&amp;</c-> <c- n>error</c-><c- p>()</c-> <c- o>&amp;</c-><c- p>;</c->
    <c- k>const</c-> <c- n>E</c-><c- o>&amp;</c-> <c- n>error</c-><c- p>()</c-> <c- k>const</c-><c- o>&amp;</c-><c- p>;</c->
    <c- n>E</c-><c- o>&amp;&amp;</c-> <c- n>error</c-><c- p>()</c-> <c- o>&amp;&amp;</c-><c- p>;</c->
    <c- k>const</c-> <c- n>E</c-><c- o>&amp;&amp;</c->  <c- n>error</c-><c- p>()</c-> <c- k>const</c-><c- o>&amp;&amp;</c-><c- p>;</c->
<c- nl>private</c-><c- p>:</c->
    <c- n>E</c-> <c- n>val</c-><c- p>;</c-> <c- c1>// exposition only</c->
<c- p>};</c->
</pre>
   <p class="issue" id="issue-ca33ce68"><a class="self-link" href="#issue-ca33ce68"></a> Wondering if we just need an <code class="highlight"><c- k>const</c-> <c- o>&amp;</c-></code> overload as we do for <code class="highlight"><c- n>system_error</c-></code>.</p>
   <p>The template class <code class="highlight"><c- n>bad_expected_access</c-></code> defines the type of objects thrown as
exceptions to report the situation where an attempt is made to access the value
of <code class="highlight"><c- n>expected</c-></code> object that contains an <code class="highlight"><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code>.</p>
<pre class="language-c++ highlight"><c- n>bad_expected_access</c-><c- o>::</c-><c- n>bad_expected_access</c-><c- p>(</c-><c- n>E</c-> <c- n>e</c-><c- p>);</c->
</pre>
   <p><em>Effects</em>: Initialize <code class="highlight"><c- n>val</c-></code> with <code class="highlight"><c- n>e</c-></code>.</p>
   <p><em>Postconditions</em>: <code class="highlight"><c- n>what</c-><c- p>()</c-></code> returns an implementation-defined NTBS.</p>
<pre class="language-c++ highlight"><c- k>const</c-> <c- n>E</c-><c- o>&amp;</c-> <c- n>error</c-><c- p>()</c-> <c- k>const</c-><c- o>&amp;</c-><c- p>;</c->
<c- n>E</c-><c- o>&amp;</c-> <c- n>error</c-><c- p>()</c-> <c- o>&amp;</c-><c- p>;</c->
</pre>
   <p><em>Returns</em>: <code class="highlight"><c- n>val</c-><c- p>;</c-></code></p>
<pre class="language-c++ highlight"><c- n>E</c-><c- o>&amp;&amp;</c-> <c- n>error</c-><c- p>()</c-> <c- o>&amp;&amp;</c-><c- p>;</c->
<c- k>const</c-> <c- n>E</c-><c- o>&amp;&amp;</c-> <c- n>error</c-><c- p>()</c-> <c- k>const</c-> <c- o>&amp;&amp;</c-><c- p>;</c->
</pre>
   <p><em>Returns</em>: <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>move</c-><c- p>(</c-><c- n>val</c-><c- p>);</c-></code></p>
<pre class="language-c++ highlight"><c- n>virtual</c-> <c- k>const</c-> <c- b>char</c-><c- o>*</c-> <c- nf>what</c-><c- p>()</c-> <c- k>const</c-> <c- n>noexcept</c-> <c- n>override</c-><c- p>;</c->
</pre>
   <p><em>Returns</em>: An implementation-defined NTBS.</p>
   <h3 class="heading settled" data-level="1.20" id="expected.bad_expected_access_base"><span class="secno">1.20. </span><span class="content">�.�.7 Class <code class="highlight"><c- n>bad_expected_access</c-><c- o>&lt;</c-><c- b>void</c-><c- o>></c-></code> [<em>expected.bad_expected_access_base</em>]</span><a class="self-link" href="#expected.bad_expected_access_base"></a></h3>
<pre class="language-c++ highlight"><c- n>template</c-> <c- o>&lt;></c->
<c- n>class</c-> <c- n>bad_expected_access</c-><c- o>&lt;</c-><c- b>void</c-><c- o>></c-> <c- o>:</c-> <c- n>public</c-> <c- n>exception</c-> <c- p>{</c->
<c- nl>public</c-><c- p>:</c->
    <c- n>explicit</c-> <c- n>bad_expected_access</c-><c- p>();</c->
<c- p>};</c->
</pre>
   <h3 class="heading settled" data-level="1.21" id="expected.unexpect"><span class="secno">1.21. </span><span class="content">�.�.8 <code class="highlight"><c- n>unexpect</c-></code> tag [<em>expected.unexpect</em>]</span><a class="self-link" href="#expected.unexpect"></a></h3>
<pre class="language-c++ highlight"><c- k>struct</c-> <c- n>unexpect_t</c-> <c- p>{</c->
    <c- n>explicit</c-> <c- n>unexpect_t</c-><c- p>()</c-> <c- o>=</c-> <c- k>default</c-><c- p>;</c->
<c- p>};</c->
<c- kr>inline</c-> <c- n>constexpr</c-> <c- n>unexpect_t</c-> <c- n>unexpect</c-><c- p>{};</c->
</pre>
   <h2 class="heading settled" data-level="2" id="qq"><span class="secno">2. </span><span class="content">Open Questions</span><a class="self-link" href="#qq"></a></h2>
   <p><code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>expected</c-></code> is a vocabulary type with an opinionated design and a proven
record under varied forms in a multitude of codebases. Its current form has
undergone multiple revisions and received substantial feedback, falling roughly
in the following categories:</p>
   <ol>
    <li data-md>
     <p><strong>Ergonomics</strong>: is this <em>the right way</em> to expose such functionality?</p>
    <li data-md>
     <p><strong>Disappointment</strong>: should we expose this in the Standard, given C++'s
 existing error handling mechanisms?</p>
    <li data-md>
     <p><strong>STL usage</strong>: should the Standard Template Library adopt this class, at
 which pace, and where?</p>
   </ol>
   <p>LEWG and EWG have nonetheless reached consensus that a class of this general
approach is probably desirable, and the only way to truly answer these questions
is to try it out in a TS and ask for explicit feedback from developers. The
authors hope that developers will provide new information which they’ll be able
to communicate to the Committee.</p>
   <p>Here are open questions, and questions which the Committee thinks are settled
and which new information can justify revisiting.</p>
   <h3 class="heading settled" data-level="2.1" id="ergo"><span class="secno">2.1. </span><span class="content">Ergonomics</span><a class="self-link" href="#ergo"></a></h3>
   <ol>
    <li data-md>
     <p>Name:</p>
     <ul>
      <li data-md>
       <p>Is <code class="highlight"><c- n>expected</c-></code> the right name?</p>
      <li data-md>
       <p>Does it express intent both as a consumer and a producer?</p>
     </ul>
    <li data-md>
     <p>Is <code class="highlight"><c- n>E</c-></code> a salient property of <code class="highlight"><c- n>expected</c-></code>?</p>
    <li data-md>
     <p>Is <code class="highlight"><c- n>expected</c-><c- o>&lt;</c-><c- b>void</c-><c- p>,</c-> <c- n>E</c-><c- o>></c-></code> clear on what it expresses as a return type?</p>
    <li data-md>
     <p>Would it make sense for <code class="highlight"><c- n>expected</c-></code> to support containing <em>both</em> <code class="highlight"><c- n>T</c-></code> and <code class="highlight"><c- n>E</c-></code> (in some designs, either one of them being optional), or is this use case better handled by a separate proposal?</p>
    <li data-md>
     <p>Is the order of parameters <code class="highlight"><c- o>&lt;</c-><c- n>T</c-><c- p>,</c-> <c- n>E</c-><c- o>></c-></code> appropriate?</p>
    <li data-md>
     <p>Is usage of <code class="highlight"><c- n>expected</c-></code> "viral" in a codebase, or can it be adopted incrementally?</p>
    <li data-md>
     <ul>
      <li data-md>
       <p>Missing <code class="highlight"><c- n>expected</c-><c- o>&lt;</c-><c- n>T</c-><c- p>,</c-><c- n>E</c-><c- o>>::</c-><c- n>emplace</c-></code> for <code class="highlight"><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code>.</p>
      <li data-md>
       <p>The in-place construction from a <code class="highlight"><c- n>unexpected</c-><c- o>&lt;</c-><c- n>E</c-><c- o>></c-></code> using the <code class="highlight"><c- n>unexpet</c-></code> tag doesn’t conveys the in-place nature of this constructor.</p>
      <li data-md>
       <p>Do we need in-place using indexes, as variant?</p>
     </ul>
    <li data-md>
     <p>Comparisons:</p>
     <ul>
      <li data-md>
       <p>Are <code class="highlight"><c- o>==</c-></code> and <code class="highlight"><c- o>!=</c-></code> useful?</p>
      <li data-md>
       <p>Should other comparisons be provided?</p>
      <li data-md>
       <p>What usages of <code class="highlight"><c- n>expected</c-></code> mandate putting instances in a <code class="highlight"><c- n>map</c-></code>, or other such container?</p>
      <li data-md>
       <p>Should <code class="highlight"><c- n>hash</c-></code> be provided?</p>
      <li data-md>
       <p>What usages of <code class="highlight"><c- n>expected</c-></code> mandate putting instances in an <code class="highlight"><c- n>unordered_map</c-></code>, or other such container?</p>
      <li data-md>
       <p>Should <code class="highlight"><c- n>expected</c-><c- o>&lt;</c-><c- n>T</c-><c- p>,</c-> <c- n>E</c-><c- o>></c-></code> always be comparable if <code class="highlight"><c- n>T</c-></code> is comparable, even if <code class="highlight"><c- n>E</c-></code> is not comparable?</p>
     </ul>
    <li data-md>
     <p>Error type <code class="highlight"><c- n>E</c-></code>:</p>
     <ul>
      <li data-md>
       <p>Have <code class="highlight"><c- n>expected</c-><c- o>&lt;</c-><c- n>T</c-><c- p>,</c-> <c- b>void</c-><c- o>></c-></code> and <code class="highlight"><c- n>unexpected</c-><c- o>&lt;</c-><c- b>void</c-><c- o>></c-></code> a sense?</p>
      <li data-md>
       <p><code class="highlight"><c- n>E</c-></code> template parameter has no default. Should it?</p>
      <li data-md>
       <p>Should <code class="highlight"><c- n>expected</c-></code> be specialized for particular <code class="highlight"><c- n>E</c-></code> types such as <code class="highlight"><c- n>exception_ptr</c-></code> and how?</p>
      <li data-md>
       <p>Should <code class="highlight"><c- n>expected</c-></code> handle <code class="highlight"><c- n>E</c-></code> types with a built-in "success" value any differently and how?</p>
      <li data-md>
       <p><code class="highlight"><c- n>expected</c-></code> is not implicitly constructible from an <code class="highlight"><c- n>E</c-></code>, even when unambiguous from <code class="highlight"><c- n>T</c-></code>, because as a vocabulary type it wants unexpected error construction to be verbose, and require hopping through an <code class="highlight"><c- n>unexpected</c-></code>. Is the verbosity extraneous?</p>
     </ul>
    <li data-md>
     <p>Does usage of this class cause a meaningful performance impact compared to using error codes?</p>
    <li data-md>
     <p>The accessor design offers a terse unchecked dereference operator (expected to be used alongside the implicit <code class="highlight"><c- b>bool</c-></code> conversion), as well as <code class="highlight"><c- n>value</c-><c- p>()</c-></code> and <code class="highlight"><c- n>error</c-><c- p>()</c-></code> accessors which are checked. Is that a gotcha, or is it similar enough to classes such as <code class="highlight"><c- n>optional</c-></code> to be unsurprising?</p>
    <li data-md>
     <p>Is <code class="highlight"><c- n>bad_expected_access</c-></code> the right thing to throw?</p>
    <li data-md>
     <p>Should some members be <code class="highlight"><c- n>nodiscard</c-></code>?</p>
   </ol>
   <h3 class="heading settled" data-level="2.2" id="dis"><span class="secno">2.2. </span><span class="content">Disappointment</span><a class="self-link" href="#dis"></a></h3>
   <p>C++ already supports exceptions and error codes, <code class="highlight"><c- n>expected</c-></code> would be a third
kind of error handling.</p>
   <ol>
    <li data-md>
     <p>where does <code class="highlight"><c- n>expected</c-></code> work better than either exceptions or error handling?</p>
    <li data-md>
     <p><code class="highlight"><c- n>expected</c-></code> was designed to be particularly well suited to APIs which require their immediate caller to consider an error scenario. Do it succeed in that purpose?</p>
    <li data-md>
     <p>Do codebases successfully compose these three types of error handling?</p>
    <li data-md>
     <p>Is debuggability any harder?</p>
    <li data-md>
     <p>Is it easy to teach C++ as a whole with a third type of error handling?</p>
   </ol>
   <h3 class="heading settled" data-level="2.3" id="stl"><span class="secno">2.3. </span><span class="content">STL Usage</span><a class="self-link" href="#stl"></a></h3>
   <ol>
    <li data-md>
     <p>Should <code class="highlight"><c- n>expected</c-></code> be used in the STL at the same time as it gets standardized?</p>
    <li data-md>
     <p>Where, considering <code class="highlight"><c- n>std2</c-></code> may be a good place to change APIs?</p>
   </ol>
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  <h2 class="no-num no-ref heading settled" id="references"><span class="content">References</span><a class="self-link" href="#references"></a></h2>
  <h3 class="no-num no-ref heading settled" id="informative"><span class="content">Informative References</span><a class="self-link" href="#informative"></a></h3>
  <dl>
   <dt id="biblio-p0323r4">[P0323r4]
   <dd>Vicente Botet, JF Bastien. <a href="https://wg21.link/p0323r4">std::expected</a>. 26 November 2017. URL: <a href="https://wg21.link/p0323r4">https://wg21.link/p0323r4</a>
   <dt id="biblio-p0323r5">[P0323r5]
   <dd>Vicente Botet, JF Bastien. <a href="https://wg21.link/p0323r5">std::expected</a>. 8 February 2018. URL: <a href="https://wg21.link/p0323r5">https://wg21.link/p0323r5</a>
  </dl>
  <h2 class="no-num no-ref heading settled" id="issues-index"><span class="content">Issues Index</span><a class="self-link" href="#issues-index"></a></h2>
  <div style="counter-reset:issue">
   <div class="issue"> Wondering if we just need an <code class="highlight"><c- k>const</c-> <c- o>&amp;</c-></code> overload as we do for <code class="highlight"><c- n>system_error</c-></code>.<a href="#issue-ca33ce68"> ↵ </a></div>
  </div>